The Base of the 

Upper Keweenawan, 

Michigan and 

Wisconsin

GEOLOGICAL SURVEY BULLETIN 1354-F

The Base of the 

Upper Keweenawan, 

Michigan and 

Wisconsin

By WALTER S. WHITE

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1354-F

A proposal to adopt the top of the Copper 

Harbor Conglomerate as the base of the 

upper Keweenawan in the Lake Superior 

region

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 72-75175

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402 - Price 25 cents (paper cover)

Stock Number 24pl-2099
CONTENTS

Page

Abstract _____________________ _..- Fl

Introduction _______________ - - 1

Acknowledgments __ _____ __ 3

Original definition and usage ______ _ 4

Oronto Group _____________________-.____ _ 7

Alternatives for stratigraphic placement of the base of the upper

Keweenawan __________________.___ _ _ 7

Top and bottom of the Copper Harbor Conglomerate as unconformities ________________________.____________ 8

Base of the Copper Harbor Conglomerate __________ _ 9

Top of the Copper Harbor Conglomerate _____________ 11

Paleomagnetic data ______________________________ 14

Seismic data ________________________..__________ 15

Summary and recommendation ________________________ 16

References _____________________.______._________ 20

ILLUSTRATIONS

Page

FIGURE 1. Distribution of the Copper Harbor Conglomerate and included mafic lava members _________________ F2

2. Stratigraphic section of the Copper Harbor Conglomerate _ 3

3. Longitudinal stratigraphic section of Keweenawan rocks

below the base of the Nonesuch Shale ________ _ 5

4. Mean directions of magnetization for some Keweenawan

rocks ________________________________ 13

5. Proposed nomenclature for middle and upper Keweenawan

rocks _^________________________^_______________ 19

TABLE

Page

TABLE 1. Compressional wave velocities (km/sec) for selected Keweenawan stratigraphic units, Lake Superior region _ F16

ill

CONTRIBUTIONS TO STRATIGRAPHY

THE BASE OF THE UPPER KEWEENAWAN, 

MICHIGAN AND WISCONSIN

By WALTER S. WHITE

ABSTRACT

The top of the Copper Harbor Conglomerate (base of Nonesuch Shale) 

is a more satisfactory boundary between upper and middle Keweenawan rocks 

in northern Michigan and adjacent parts of Wisconsin than the various 

horizons that have been used hitherto without stratigraphic consistency from 

place to place. Irving's original boundary (1883) cannot be followed away 

from the Keweenaw Peninsula. The top of the Copper Harbor Conglomerate 

comes closer to marking the close of Keweenawan volcanism than other major 

boundaries and actually adheres more closely to Irving's original concept 

than the boundary that he himself chose. The top of the Copper Harbor 

Conglomerate is also more satisfactory from a practical standpoint because, 

thanks to exploration for copper at the base of the Nonesuch Shale, no other 

major stratigraphic boundary in the Keweenawan province is so precisely 

located over so large a fraction of its total outcrop trace. This paper proposes 

that the top of the Copper Harbor Conglomerate be adopted as the base of 

the upper Keweenawan and of the Oronto Group.

INTRODUCTION

The base of the "upper Keweenawan," a term applied to certain 

rocks of Precambrian Y ' age in the Lake Superior region, has not 

been placed at the same stratigraphic horizon by all who have had 

occasion to use the term. Any of the possible definitions or redefinitions that might be adopted would be arbitrary, but light shed 

on the question by geologic and geophysical data gathered in 

recent decades now makes one of these choices seem more meaningful and more practical than the others.

1 An interim scheme for the subdivision of Precambrian time, recently adopted by the U.S. 

Geological Survey:

Precambrian Z = base of Cambrian to 800 m.y. 

Precambrian Y 800 m.y. to 1,600 m.y. 

Precambrian X = l,600 m.y. to 2,500 m.y. 

Precambrian W = older than 2,500 m.y.

Fl
88°30'

47°30'

FIGURE 1. Distribution of the Copper Harbor Conglomerate and included m

sula of northern Michigan. Discontinuous lava units too thin to show w

lowest mafic lava member depicted on the map in the area west and north 

and Copper Harbor. Geology from 1:24,000 geologic quadrangle maps (C

White, 1955; Cornwall and Wright, 1954, 1956a, b; Davidson and others, 

White and Wright, 1956; Wright and Cornwall, 1954).
THE BASE OF THE UPPER KEWEENAWAN

ACKNOWLEDGMENTS

F3

I am very much indebted to N. K. Huber, who pointed out to me 

that when my colleagues and I (White and others, 1953) redefined

FEET 

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Outcrop of rocks above 

dashed line is covered 

by Lake Superior east 

of longitude 88°24'

OUTER CONGLOMERATE

A

LAKE SHORE TRAP

GREAT 

CONGLOMERATE

z

0 

(/)

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(not named) g 

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PORTAGE LAKE 

LAVA SERIES

FIGURE 2. Stratigraphic section of the Copper Harbor Conglomerate in 

the vicinity of Copper Harbor (from data of Cornwall, 1954b, c, 1955).
F4 CONTRIBUTIONS TO STRATIGRAPHY

the base of the upper Keweenawan on the Keweenaw Peninsula, 

we did not take formal notice of the departure from Irving's 

(1883) original definition, which was very explicit in his type 

area. Huber encouraged me to remedy this oversight, and this 

paper, though quite different from what I set out to write, is the 

result. I owe much to my colleagues Henry R. Cornwall and the 

late J. C. Wright for the years of joint endeavor that provided 

much of the background for this paper. And finally, the stratigraphic relations shown west of long. 89° 15' in figure 3, so important a part of the argument in this paper, would have been most 

imperfectly reconstructed without the results from recent unpublished mapping by E. R. Brooks, H. A. Hubbard, R. F. Johnson, 

and J. T. Wilband (White and others, 1971), as can be readily 

seen by comparison of figure 3 with an earlier attempt to draw 

a similar section (White and Wright, 1960, fig. 3.2).

A most constructive critical review of the original manuscript 

by N. K. Huber led to substantial revision of parts of the text.

ORIGINAL DEFINITION AND USAGE

The reason for the problem has its roots in Irving's (1883) 

definition of what he called the "Upper Division" of the Keweenawan. The type locality for his classification is on the north shore 

of the Keweenaw Peninsula, in a belt extending a few miles east 

and west from Copper Harbor (fig. 1). Figure 2 shows a stratigraphic section of the Copper Harbor Conglomerate in this area 

and the names that have been applied to the various units by 

Irving (left-hand column) and more recent investigators (righthand column) (see, especially, Cornwall, 1954b, c; 1955).

Irving (1883, p. 152) placed the boundary between his "Upper 

Division" and "Lower Division" 2 of the "Keweenaw Series" at 

the, "base of the outer conglomerate of Keweenaw Point which 

[as he believed] corresponds to the top of the upper amygdaloid of 

the Porcupines, and to the base of the great conglomerate of the 

Montreal, and which is above any known occurrence of eruptive 

matter." This boundary was a very reasonable choice at the time 

and was later accepted by others (for example, Lane, 1911, p. 37-

- The rocks immediately below the base of upper Keweenawan have been called "lower 

Keweenawan" (lower division of the Keweenawan) by some authors and "middle Keweenawan" 

by others. For the purposes of this paper, it makes no difference which usage is followed, 

but it should be pointed out that a threefold division of the Keweenawan appears far more 

useful than a twofold in the light of what is now known about the stratigraphy throughout 

the Lake Superior region (Van Hise and Leith, 1911, p. 366-367; Halls, 1966, p. 5; Hubbard, 

1968; Books, 1968).
Montreal River Ironwood WISCONSIN [MICHIGAN! 9P

. --"" Stratigrap

^-"^-Rocks below this line are covered Of Keween

,/' by younger rocks, and their 

lithology is not known

EXPL

Index map of part of Lake Superior region showing 

approximate line of longitudinal Stratigraphic 

section (dashed line)

Unnamed formation 

Major felsic members 

shown by "v" pattern

FIGURE 3. Longitudinal Stratigraphic section of Keweenawan rocks below the 

naw Point to the Montreal River. All data projected to an east-west line. Da

Series represent individual horizons that can be traced with confidence betw

lation of drill-hole sections. Thickness east of long. 89° 15' from sources list

and others (1929, pi. 15) ; thickness west of long. 89°15' calculated from u

Hubbard, R. F. Johnson, W. S. White, J. T. Wilband, and J. C. Wright.
F6 CONTRIBUTIONS TO STRATIGRAPHY

39; Van Hise and Leith, 1911, p. 413; Thwaites, 1912, p. 48 and 

geol. map) primarily for its presumed importance as the surface 

marking the close of volcanism in the region. The stratigraphic 

position of this surface of demarcation in the type area is indicated by the line labeled "A" in figures 1 and 2.

Figures 1 and 3 clearly show some of the problems that stem 

from Irving's choice. As Lane (1911, p. 39; see also Lane and 

Seaman, 1907, p. 690) clearly recognized from his own subsequent 

work, practical difficulties attend any effort to follow Irving's 

boundary away from Keweenaw Point. If the base of the upper 

Keweenawan is defined as the time-equivalent of Irving's boundary on the Keweenaw Peninsula, it does not coincide with any 

recognized lithologic unit or break beyond the point where the 

highest so-called "Lake Shore trap" of the Keweenaw Peninsula 

pinches out north of Hancock (fig. 1). There is no theoretical or 

practical reason, today, to correlate the "Lake Shore traps" of the 

Porcupine Mountain region (Wright and Lane, 1909) or of the 

Black River (Gordon and Lane, 1907, p. 430) with those of 

Keweenaw Point, and there is no way, at present, to identify beds 

in westernmost Michigan or Wisconsin, for example, that might 

be contemporaneous with the top of the "Lake Shore traps" of 

Keweenaw Point.

If, on the other hand, the base of the upper Keweenawan is 

defined as the top of the highest lava flow, regardless of stratigraphic position (which is what authors attempting to follow 

Irving rigorously have actually done in practice), its stratigraphic 

position can change abruptly by as much as 2,000 feet at places 

where the highest lava flow pinches out (fig. 3). At the many 

places where no "Lake Shore trap" flows are recognized, authors 

have placed the boundary at the top of the Portage Lake Lava 

Series.

Other problems caused by acceptance of Irving's boundary have 

only become obvious in recent decades as a result of detailed 

geologic mapping and magnetic surveys. One is that the base of 

what Irving took as his "Outer Conglomerate" of Keweenaw Point 

is actually 1,500-2,000 feet below the top of the highest lava flow 

in that area, as can be shown by geologic projection and airborne 

magnetometer survey (fig. 1). Another is that the end of volcanism was almost certainly later than the highest known lava flow; 

I have found water-laid tuff, probably representing ash falls, in 

drill core within 25 feet of the base of the Nonesuch Shale (sec. 

33, T. 55 N., R. 34 W.)
THE BASE OF THE UPPER KEWEENAWAN F7

ORONTO GROUP

Thwaites (1912, p. 48) introduced the term Oronto Group for 

"a great thickness of arkose sandstones and shales" overlying the 

lavas and underlying more quartzose sandstone formations, to 

which he gave the name Bayfield Group. Following Irving's precedent, he took the base of the Oronto Group as "the base of a thick 

conglomerate called the Outer Conglomerate, above which horizon 

no igneous rocks occur." His definition and the explanation for the 

map accompanying his report clearly equate the base of the 

Oronto Group and the base of the upper Keweenawan, and this 

identity seems to have been accepted by all those who have had 

occasion to use the term Oronto Group, even where there might 

be disagreement or inconsistency, from area to area, about where 

the boundary should be placed stratigraphically. It should be recognized, therefore, that any redefinition of the base of the upper 

Keweenawan should apply also to the base of the Oronto Group.

ALTERNATIVES FOR STRATIGRAPHIC PLACEMENT OF THE BASE 

OF THE UPPER KEWEENAWAN

The name "Outer Conglomerate," used rather informally by 

Irving, has unfortunately become formalized by subsequent usage, 

despite the fact that, from a practical standpoint, its base cannot 

be followed west from the Keweenaw Peninsula. Because the 

"Outer Conglomerate" has only local significance it seems inappropriate both as a formal stratigraphic name and as unit defining 

the base of the upper Keweenawan. Lane (1911, p. 37-39) clearly 

recognized that the discontinuity of the lavas known as the "Lake 

Shore traps" made it impractical to separate the "Outer" and 

"Great Conglomerates" outside the Keweenaw Peninsula, and he 

therefore collectively grouped all conglomerates above the Portage 

Lake Lava Series and below the Nonesuch Shale into the "Copper 

Harbor Conglomerates." Lane continued to accept the base of the 

"Outer Conglomerate" as the base of the upper Keweenawan, 

however, and thus the lumping of Irving's "Outer" and "Great 

Conglomerate" into a single formation has, as Lane (1911, p. 39) 

recognized, the disadvantage of placing the base of the upper 

Keweenwan within a formation.

From a hierarchical point of view, it seems most undesirable to 

have a boundary of major rank fall within a unit of lesser rank. 

Inasmuch as the base of the upper Keweenawan (and of the 

Oronto Group) does fall within a formation that cannot be subdivided on any theoretical or practical grounds that are valid and
F8 CONTRIBUTIONS TO STRATIGRAPHY

consistent on a regional basis, the most obvious alternatives are to 

place the base of the upper Keweenawan at either the top or base 

of the Copper Harbor Conglomerate.

TOP AND BOTTOM OF THE COPPER HARBOR CONGLOMERATE AS UNCONFORMITIES

If either the top or bottom of the Copper Harbor Conglomerate, 

but not both, were known to be a pronounced unconformity, the 

unconformable contact should, with little question, be adopted as 

the base of the upper Keweenawan. On this basis, unfortunately, 

there is little to choose between them.

Both boundaries are more or less gradational. The conglomerate and sandstone beds between lava flows of the Portage Lake 

Lava Series differ little from those of the Copper Harbor Conglomerate, both on the Keweenaw Peninsula and on Isle Royale (Lane, 

1898; Huber, 1971). Sedimentary beds are more abundant in the 

uppermost 1,000 feet or so of the Portage Lake Lava Series than 

below, and the choice of the top of the highest lava flow as the 

formation boundary, though logical and practical, is quite arbitrary. The transition between the formations reflects a gradual 

decrease in volcanic activity and growing dominance of a sedimentary regime rather than an abrupt time or environmental 

break.

Similarly, sandstone and dark-gray siltstone to shale are interbedded and interlaminated in the lowermost 20 feet of the Nonesuch Shale, and the basal contact (top of the Copper Harbor Conglomerate) is arbitrarily placed at the base of the lowest thick 

(several feet) unit containing dark-gray siltstone and shale. This 

boundary does reflect a relatively abrupt change from a subaerial 

to a shallow subaqueous environment.

Both boundaries are only slightly transgressive. Maps of part 

of the Keweenaw Peninsula by Cornwall (1954b) and Cornwall 

and Wright (1954) suggest that the stratigraphic position of the 

base of the Copper Harbor Conglomerate may locally rise toward 

the west, but the rate of rise is very small. Even where the Copper 

Harbor Conglomerate laps up on the unnamed formation (fig. 3), 

the contact does not appear to be notably unconformable and may 

have much intertonguing. Gradual transgression of the base of the 

Nonesuch Shale is clearly shown in north-south sections of the 

base of that formation in the Porcupine Mountain region (White 

and Wright, 1966, fig. 2), but it is barely detectable without considerable vertical exaggeration.

It is conceivable that the uppermost beds of the Copper Harbor 

Conglomerate represent sands reworked by the waters in which
THE BASE OF THE UPPER KEWEENAWAN F9

the Nonesuch Shale was deposited and that the apparent nearconformity of these beds masks or blurs a more profound angular 

unconformity between the Nonesuch Shale and the Copper Harbor 

Conglomerate as a whole. Stratigraphic relations within the 

Copper Harbor Conglomerate are not well known because of poor 

exposures and few drill holes, but meager information that is 

available suggests that there is no significant angular unconformity between the two. The relations shown in figure 3, particularly near Houghton, suggest that much of the local angular discordance between the Portage Lake Lava Series and the Nonesuch Shale is due to tectonic movements during rather than before 

or after Copper Harbor time.

Finally, neither boundary represents any profound change in 

the basic pattern of sediment dispersal, for as Hamblin and 

Horner (1961, p. 210) point out, the same pattern, implying highlands to the south or southeast of the western Lake Superior 

region, persisted from Portage Lake through Freda time. Hite 

(1968) reached a similar conclusion for the Copper Harbor Conglomerate and higher formations that he studied in northeastern 

Wisconsin.

In summary, therefore, the magnitude of the unconformities 

represented by the top and base, respectively, of the Copper 

Harbor Conglomerate provides little reason for considering one 

of the contacts more suitable than the other to be taken as the 

base of the upper Keweenawan. Some other basis must be sought.

BASE OF THE COPPER HARBOR CONGLOMERATE

The principal argument for placing the base of the upper 

Keweenawan at the base of the Copper Harbor Conglomerate is 

the weight of prior usage, even though this usage has commonly 

involved an unwitting departure from the original definition. In 

the many areas where no "Lake Shore traps" are recognized, 

authors have unfailingly placed the boundary at the base of the 

Copper Harbor Conglomerate (for example, Van Hise and Leith, 

1911, pi. 1; Leith and others, 1935, pi. 1). Some authors, particularly in Wisconsin (Thwaites, 1912; Aldrich, 1929; Tyler and 

others, 1940; Ostrom, 1967; Hite, 1968), have semantically resolved this departure from Irving's definition by simply using the 

name Outer Conglomerate for all the rocks between the Portage 

Lake Lava Series and the Nonesuch Shale. Although for Wisconsin, in particular, this correlation is not inconceivable, the relations shown in figure 3 do not provide much support for it, and 

the correlation is certainly not valid in areas such as that shown 

in the southwestern part of figure 1.
F10 CONTRIBUTIONS TO STRATIGRAPHY

On the Keweenaw Peninsula, this usage adopted elsewhere cannot be reconciled with Irving's usage, and a choice must be made 

between the two. White, Cornwall, and Swanson (1953) chose to 

follow the usage accepted for the region as a whole rather than 

Irving's definition when, on maps of the Keweenaw Peninsula, 

they placed the base of the upper Keweenawan at the base of 

Lane's (1911) "Copper Harbor Conglomerates." The more conventional singular form was used by White (1952) and White, 

Cornwall, and Swanson (1953) when they adopted Lane's term 

as a formation name. Several more recent authors (Hamblin and 

Horner, 1961; Hamblin, 1961; Halls, 1966; Kelley, 1968) have 

followed suit, using the term Copper Harbor Conglomerate for 

the whole conglomerate sequence and accepting the top of the 

Portage Lake Lava Series as the base of the upper Keweenawan 

on the Keweenaw Peninsula as well as in the areas where this 

usage had become more or less established.

From the foregoing, it might appear simplest, therefore, to 

follow this revised usage that has gained general acceptance, and 

to place the base of the upper Keweenawan at the top of the main 

body of lavas, including within the upper Keweenawan those 

flows within the Copper Harbor Conglomerate that have been 

called "Lake Shore traps." Recent work in western Michigan, 

however, has greatly complicated this otherwise straightforward 

solution.

As shown by figure 3, the horizon that marks the top of the 

Portage Lake Lava Series can be located very closely by reference 

to the internal stratigraphy of that formation (Butler, Burbank, 

and others, 1929, pi. 15; White, 1968, fig. 3). As this horizon is 

followed southwestward from the Keweenaw Peninsula, it passes 

beneath an unnamed formation consisting of a thick series of 

felsic and generally nonophitic mafic flows (fig. 3). In the region 

south of the Porcupine Mountains, this overlying sequence of 

flows attains a thickness of at least 8,000 feet, whereas the Copper 

Harbor Conglomerate shows complementary thinning; in places, 

the total thickness of sandstone and conglomerates of the Copper 

Harbor is less than 200 feet. The sequence of flows between the 

top of the Portage Lake Lava Series and the overlying Copper 

Harbor Conglomerate appears to be a volcanic pile (White and 

Wright, 1960), and the rocks just below this pile are probably 

more or less contemporaneous with rocks just below the base of 

the Copper Harbor Conglomerate on Keweenaw Peninsula.

This new development materially affects the attractiveness of 

the base of the Copper Harbor Conglomerate as a location for the
THE BASE OF THE UPPER KEWEENAWAN Fll

base of the upper Keweenawan. On Keweenaw Peninsula and 

probably in northeastern Wisconsin, the base of the Copper Harbor 

Conglomerate and the top of the Portage Lake Lava Series are one 

and the same contact. In the Porcupine Mountain region, they are 

not, and there is a difference between adopting the base of the 

Copper Harbor Conglomerate, on the one hand, or the top of the 

Portage Lake Lava Series, on the other, as the base of the upper 

Keweenawan. Exposures are poor in this region, and the amount 

of interfingering between the Copper Harbor Conglomerate and 

the unnamed formation is not yet known. The question of whether 

or not the unnamed formation is contemporaneous with any or 

most of the Copper Harbor Conglomerate is, therefore, unresolved. The complementary changes in thickness shown in figure 

3 strongly suggest at least some overlap in time. If the base of the 

upper Keweenawan is drawn to approximate a time line, therefore, as it probably should be, it should be drawn at the top of 

the Portage Lake Lava Series. The boundary between a predominantly extrusive sequence below and a predominantly sedimentary sequence above, although convenient for mapping purposes, 

is seen to have little meaning as a time line. The same is true 

farther west in Wisconsin. The Portage Lake Lava Series, for 

example, cannot yet be correlated with the sequence of lavas 

immediately below the Copper Harbor Conglomerate southwest 

of Ashland, Wis., (fig. 3, index map). The boundary between the 

extrusive and overlying sedimentary sequence, now commonly 

accepted there as the base of the upper Keweenawan, therefore, 

cannot be assumed to be contemporaneous with the base of the 

Copper Harbor Conglomerate on the Keweenaw Peninsula.

Although the problem of approximating a time line can be 

resolved, at least for the Porcupine Mountain area, by drawing 

the boundary at the top of the Portage Lake Lava Series, beneath 

the unnamed formation (fig. 3), this solution has two major drawbacks. First, a sequence of lava flows as much as 8,000 feet thick 

is included with the upper Keweenawan rocks, and any significance the boundary might have as a reflection of change is lost. 

Secondly, as a practical matter, it may prove difficult to follow 

this boundary with any accuracy through areas of poor exposure 

west of long. 89°50' W. The boundary as drawn in figure 3 is 

based to a considerable extent on a projection parallel to the 

traces of aeromagnetic anomalies (Zietz and Kirby, 1971).

TOP OF THE COPPER HARBOR CONGLOMERATE

The top of the Copper Harbor Conglomerate has much to rec-
F12 CONTRIBUTIONS TO STRATIGRAPHY

ommend it as an alternative location for the base of the upper 

Keweenawan.

First, as a time line, this contact comes very close indeed to 

fulfilling Irving's concept that the base of the upper Keweenawan 

should mark the close of active volcanism in the Lake Superior 

region. Northwest of Calumet (fig. 1), the boundary that Irving 

(1883, pi. 17) did draw is only 300 feet stratigraphically below 

the Nonesuch Shale. Lava flows and tuff beds almost at the top 

of the Copper Harbor Conglomerate in the Keweenaw Peninsula 

area show that volcanism persisted through almost all of Copper 

Harbor time, even though this cannot be demonstrated in most 

areas because the flows themselves did not cover all parts of the 

sedimentary basin.

Second, the top of the Copper Harbor Conglomerate makes a 

better boundary than the base for practical reasons. Even though 

the Nonesuch Shale is not well exposed in most areas, the occurrence of copper at the base of that formation has encouraged a 

great deal of exploratory drillling in recent years, and the location 

of the intersection of the top of the Copper Harbor Conglomerate 

(base of Nonesuch Shale) with the bedrock surface is now known 

within a few feet to tens of feet over large areas and within 500 

feet at most places. Drilling by the Bear Creek Mining Co. has 

even delineated the approximate trace of this boundary throughout the area of deep drift cover south and west of Ashland, Wis., 

(Moerlein, 1963; White, 1966). Today, at least, no other major 

stratigraphic boundary in the entire Keweenawan province is so 

precisely located over so large a fraction of the total length of its 

outcrop (or suboutcrop).

The location of the base of the Copper Harbor Conglomerate, 

on the other hand, is much less precisely known. It can be located 

magnetically within a few tens or, at most, hundreds of feet in 

many areas of poor exposure because of the good magnetic contrast between many mafic lava flows and sedimentary rock. In 

areas of fairly deep overburden, however, magnetic methods give 

inconclusive results where the rocks near the base of the Copper 

Harbor Conglomerate consist of an alternation of thin lava flows 

and sandstones, as they do in many places. And where the rocks 

beneath the lowest thick conglomerate beds are felsic flows, as 

they are in much of western Ontonagon County, attempts to 

locate the boundary magnetically have proved fruitless.

Third, the top of the Copper Harbor Conglomerate represents a 

somewhat more pronounced lithologic change than the base, at
THE BASE OF THE UPPER KEWEENAWAN F13

least in some areas. The base, to be sure, represents a very large 

change in the ratio of effusive rocks to relatively coarse grained

EXPLANATION

Dubois (1962) 

and Books(1968)

Vincenz and 

Yaskawa (1968)

A

K. G. Books (unoub. data, 

1971)

FIGURE 4. Mean directions of magnetization for some 

Keweenawan rocks. A, Portage Lake Lava Series, with 

radius of confidence circle (95 percent) (Books, 1968, 

table 1) ; B, Copper Harbor Conglomerate, sandstones 

and lavas, with radius of confidence circle (DuBois, 

1962, table 18) ; C, Copper Harbor Conglomerate, mean 

of 13 samples of lava (calculated from data of DuBois, 

1962, table 4) ; D, Nonesuch Shale and Freda Sandstone, with radius of confidence circle (DuBois, 1962, 

table 18) ; E, Portage Lake Lava Series, mean of 14 

site means (Vincenz and Yaskawa, 1968, table 2) ; F, 

lavas from Copper Harbor Conglomerate, mean of six 

site means (Vincenz and Yaskawa, 1968, table 2) ; G, 

Nonesuch Shale and Freda Sandstone, mean of five site 

means (Vincenz and Yaskawa, 1968, table 2) ; H, J, 

and K, lavas from Copper Harbor Conglomerate, individual site means, five samples per site (K. G. Books, 

unpub. data). Directions are recalculated to values that 

equivalent dipole would produce at lat 45° N. long 

90° W. Equal-area projection, lower hemisphere, northwest quadrant.
F14 CONTRIBUTIONS TO STRATIGRAPHY

sedimentary rocks, but both these constituents are found above 

and below the contact. The top, on the other hand, marks a boundary above which no effusive rocks are known to occur and below 

which the amount of gray siltstone and shale (the predominant 

rock for several hundred feet above the contact) is vanishingly 

small. Qualitatively, therefore, the top is the boundary representing the greater lithologic change.

The main disadvantage of placing the base of the upper 

Keweenawan at the top of the Copper Harbor Conglomerate is 

that this is a significant departure from current usage, even 

though it comes much closer to fitting Irving's original boundary 

than does the current usage.

Before we proceed to a summary of pros and cons, a brief 

review of geophysical evidence relating to the choice is desirable.

PALEOMAGNETIC DATA

DuBois (1962) obtained paleomagnetic pole positions for the 

formations of concern to us here, and his results led him to conclude that the Copper Harbor Conglomerate is more closely 

related to the Portage Lake Lava Series than to the Nonesuch 

Shale and Freda Sandstone (fig. 2) ; his argument may be summarized by the observation that points B and C of figure 4 lie 

close to point A and relatively distant from point D.

More recently, Vincenz and Yaskawa (1968) have found that 

both thermal and alternating-field demagnetization materially 

flatten the direction of remanent magnetism in samples of lava 

from the Copper Harbor Conglomerate but cause very little 

change in samples of Portage Lake lavas or the younger sedimentary rocks. When the soft components of the magnetism are 

removed, the remanent direction that they obtained for lavas 

from the Copper Harbor Conglomerate (point F, fig. 4) lies 

closer to the directions for the Freda and Nonesuch (points G 

and D) than to those for the Portage Lake Lava Series (points 

E and A). They conclude from this relationship that, contrary to 

the view of DuBois, the Copper Harbor Conglomerate is closer 

paleomagnetically to the younger sedimentary rocks than to the 

Portage Lake Lava Series.

Kenneth Books has kindly provided data on paleomagnetic 

directions that he has determined for a few samples of lava from 

the Copper Harbor Conglomerate. The three sites represented by 

the data of figure 4 (points H, J, and K) are in the same general 

area as those sampled by DuBois (1962) and by Vincenz and 

Yaskawa (1968). The samples represented by H in figure 4 rep-
THE BASE OF THE UPPER KEWEENAWAN F15

resent the lower lava member of figures 1 and 2 and are from 

the same locality as DuBois' samples KH1-KH6 and Vincenz and 

Yaskawa's C1-C6. The samples represented by J and K in figure 

4 are from the SE^NW^. sec. 26, T. 57 N., R. 33 W.; they represent the same group of flows (upper lava member of fig. 2) as 

DuBois' samples KP2-KP10 and Vincenz and Yaskawa's sites 

C9-C12, both of which suites were collected about a mile farther 

to the southwest along the strike.

Samples by K. G. Books (unpub. data, 1971) were magnetically 

"washed" in alternating fields in steps up to 200 oersteds, which 

is roughly the intensity at which Vincenz and Yaskawa found 

little further change of direction. Books' direction for samples 

represented by point H is very close to Vincenz and Yaskawa's 

mean for lavas of the Copper Harbor Conglomerate (point F), 

but point K is very close to the mean direction for the Portage 

Lake Lava Series. The third of Books' site means (J, fig. 4) is 

unlike any others. These data are presented primarily to illustrate the scatter remaining in data from these particular lavas 

after magnetic "washing" scatter that will make conclusions 

about stratigraphic affinities risky until far more measurements 

have been made.

Paleomagnetic data, therefore, are still too few and equivocal 

to provide much basis for saying which geologic boundary, the 

top or the bottom of the Copper Harbor Conglomerate, marks the 

greater stratigraphic break, even if there were some basis for 

assuming that the magnetic pole wandered at a constant rate. A 

secular flattening of the paleomagnetic direction between Portage 

Lake and Freda time seems fairly well established, however, and 

this may ultimately prove very useful in stratigraphic correlations beyond the area treated here, wherever the base of the upper 

Keweenawan is placed.

SEISMIC DATA

It may also prove possible to locate the boundary, as defined, 

over large areas in the subsurface by explosion seismology. Table 

1 presents some of the results of recent work in this field that 

has been designed specifically to get the kind of information 

needed. The table does not summarize the results of that work 

but is an extract of the particular data that appear most reliable; 

that is, from the numerous velocity determinations in each study, 

I have selected only those few that appear to me to be most trustworthy and to represent the cited formation beyond any reasonable doubt, and have excluded many determinations where the
F16 CONTRIBUTIONS TO STRATIGRAPHY

TABLE 1. Compressional wave velocities (km/sec) for selected Keweenawan 

stratigraphic units, Lake Superior region

Halls and West (1971), Mooney and others 

Halls(1969), reversed refraction (1970b), unreversed 

experimental profiles 1 profiles

Bayfield Group ________ 3.9-4.7 ___ 2.8-3.4

Freda Sandstone:

Sandstone _..______ 5.1-5.5 ___ ____ 

Siltstone _________ 3.7-4.6 ___ ______

Formation velocity ____ 2 4-5 _ 3 4.2

Copper Harbor Conglomerate:

Sandstone _________ 4 5.7-6.0 ___ ______

Formation velocity ___ ___ 5.1-5.4 B 5.2-5.5

Portage Lake Lava Series

Conglomerate beds ____ 5.7-5.9 ______

Formation velocity ___ 5.9-6.1 5.8-6.1 6 5.3-5.8

1 Profiles 7-11, off Isle Royale, and 14, off Keweenaw Peninsula.

2 Very general average, assuming similar proportions of siltstone and sandstone; actual ratio 

varies considerably, silt:sand increasing toward axis of the Lake Superior basin.

3 Refractor 2,200 to 6,000 feet below surface, line 17, Bayfield County, Wis. Base of Nonesuch 

Shale should be close to 6,000 feet, by geologic projection. Main refractor in profile 16, velocity 

3.8, may also be Freda Sandstone.

4 Specimens all from Houghton Point, Isle Royale; may not be representative.

5 Main refractor line 18, and lowest refractor, line 17, Douglas and Bayfield Counties, Wis. 

Line 18 is near the axis of the Ashland syncline, and the bedrock can only be Copper Harbor 

Conglomerate. In profiles 34 and 95, lowest refractor, representing clastic filling, Twin Cities 

basin, Minnesota, has velocities of 4.7-5.1 km/sec.

6 Lowest refractor or only bedrock refractor, lines 6, 21, 23, 24, 25, 26, 33, 45, "St. Croix 

horst." It is not known that any of these rocks correlate specifically with the Portage Lake 

Lava Series; they are included simply to represent mafic lava flows.

units cannot be correlated unequivocally with formations of the 

type areas.

It is to be expected that experimental velocities would commonly exceed seismically determined velocities, particularly for 

the less well indurated sedimentary formations; there is some 

bias in sampling outcrops, which generally represent the more 

resistant elements of a formation, and, in addition, a small specimen does not represent the fractures and pores that reduce velocities in rock in place. When allowance is made for this bias, the 

experimental results fit the field determinations closely enough to 

confirm the existence of a marked difference in velocity between 

the Copper Harbor and the Freda; it is comparable, in fact, to the 

difference between the Copper Harbor and the Portage Lake Lava 

Series.

SUMMARY AND RECOMMENDATION

The base of the upper Keweenawan (and of the Oronto Group) 

could be placed at the top, within, or at the bottom of the Copper 

Harbor Conglomerate; any decision would be arbitrary. A boundary at the top of the highest lava flow, within the Copper Harbor
THE BASE OF THE UPPER KEWEENAWAN FIT

Conglomerate, has the advantage of following the original definition precisely, but this advantage is more apparent than real if 

one attempts to trace the boundary away from Irving's type area 

on Keweenaw Point. This choice has the serious disadvantage of 

placing a major stratigraphic boundary within a stratigraphic 

unit that regionally, at least, cannot be subdivided on any consistent basis.

A boundary at the base of the Copper Harbor Conglomerate is 

generally satisfactory from the standpoint of regional correlations 

and geologic mapping and has been widely used in Michigan and 

Wisconsin. Its main advantage is that it separates a dominantly 

sedimentary group of rocks from one that is dominantly volcanic 

and is, therefore, readily located if exposures are good; under 

favorable circumstances, it may also be located magnetically or 

seismically. Its main disadvantages are as follows: (1) It does 

not even approximately mark the close of volcanism in the Lake 

Superior region. (2) In the area between long. 89° and 90°20' W. 

(fig. 3), one of the two virtues it has elsewhere must be sacrificed to preserve the other: if it is regarded as an approximate 

time horizon, it should probably be carried beneath the unnamed 

formation, losing its distinctiveness as a lithologic break; if it is 

carried over the unnamed formation, it may separate lavas on one 

side from more or less contemporaneous sedimentary rocks on the 

other, losing its meaning as a time break. (3) The location of the 

base of the Copper Harbor Conglomerate is not known with anything like the same precision as the location of the top at most 

places.

The top of the Copper Harbor Conglomerate seems to make the 

best boundary between the middle and upper Keweenawan for the 

following reasons: (1) It comes closest of any of the possible 

alternatives to marking the close of volcanism as a point in time; 

it is unaffected by such local factors as the pinching out of an 

individual lava flow that happens to be the highest one at a given 

locality. (2) It does not appear to be sufficiently transgressive to 

lose its value as a time break over a very large area. (3) Thanks 

to economic interest in the copper found in rocks adjoining this 

boundary, the position of this boundary is better known for a 

higher proportion of its total strike length than the position of 

any other boundary in the Keweenawan province.

If, then, the top of the Copper Harbor Conglomerate (base of 

the Nonesuch Shale) were adopted as the base of the upper 

Keweenawan in the region between Keweenaw Point and the 

vicinity of Ashland, Wis., what would be the effect on existing
F18 CONTRIBUTIONS TO STRATIGRAPHY

literature and usage, both within and beyond the limits of this 

region ?

Rocks described and mapped as Copper Harbor Conglomerate 

would be classed as middle rather than upper Keweenawan. The 

boundaries on existing large-scale maps, showing individual formation boundaries, would be unaffected the only difference 

would be in their classification as defined by the map explanation. 

New small-scale maps, however, might differ significantly from 

existing maps where formations are lumped into large units like 

"upper Keweenawan" and Oronto Group. Locating the base of the 

upper Keweenawan (base of Oronto Group) for purposes of a 

new map would pose no problem in Michigan and Wisconsin, 

because the position of the Nonesuch Shale is well established 

throughout the region. The actual differences between new and 

old regional maps would be significant, however, because, except 

in the Keweenaw Peninsula and Porcupine Mountain region, so 

many existing regional maps, going back to Van Hise and Leith 

(1911, pi. 1), include the whole Copper Harbor Conglomerate in 

the upper Keweenawan over wide areas, rather than just the 

uppermost few hundred feet correlative with the true "Outer 

Conglomerate." For this reason, some of the areas affected are 

large, such as that underlain by the Copper Harbor Conglomerate 

on Isle Royale, and in the syncline southwest of Ashland, Wis., 

particularly west of long. 91°45' W.

Outside the region that is the main concern of this paper, the 

effect is more difficult to assess. Certain red sandstone and conglomerate formations of Minnesota, particularly in the subsurface 

within basins along the crest of the midcontinent gravity high, 

may be, in part, correlative with the Copper Harbor Conglomerate. If the Nonesuch Shale does not extend that far west, as it 

probably does not, it may prove difficult to locate the base of the 

upper Keweenawan according to the definitions suggested here. It 

may ultimately be possible to make a good separation, however, 

by a combination of lithologic and paleomagnetic data from drill 

holes and seismic data.

Data presently available strongly suggest that the paleomagnetic directions in the Freda Sandstone and Nonesuch Shale are 

much flatter than those in the Portage Lake Lava Series. These 

data offer hope that when more measurements have been made, 

the direction for rocks close to the top of the Copper Harbor 

Conglomerate will have an identifiable position on a curve for 

secular wandering of the virtual geomagnetic pole.
THE BASE OF THE UPPER KEWEENAWAN F19

The work of Mooney and others (1970a, b) indicates that velocity differences comparable with those listed in table 1 persist in 

the buried parts of the midcontinent gravity high in Minnesota. 

By means of such seismic investigations, it may ultimately be 

possible to trace the base of the upper Keweenawan, defined as 

suggested here, over large areas in the subsurface if it can be 

located at a relatively few places by lithologic or paleomagnetic 

criteria.

In the areas where the Copper Harbor Conglomerate is known 

to be present, it appears to have the form of clastic wedges that 

need not have extended far outside the elongate bowl of Portage 

Lake Lava Series that now contains them. There is no positive geologic evidence, therefore, that sedimentary formations correlative

Formations of Bayfield Group,

not differentiated here

Freda Sandstone

Nonesuch Shale

Q n

 i QLU ;3

C O

> o:

< o

DQ

Q_

O

o

o1-

2

o

or

o

 __^__^ Copper Harbor 

^X Conglomerate

jX^tjncluding rnafic lava members)

Unnamed formation /*

(volcanics) ->/

^~~~~~^^

Portage Lake Lava Series

 z.

^

>

 z.

UJ 

UJ

UJ

o:

UJ

Q_

Q_

 z.

1

UJ

LJ^LJ

LJ

Q

9

FIGURE 5. Proposed nomenclature for middle and upper Keweenawan rocks of northern Michigan and 

adjacent parts of Wisconsin.
F20 CONTRIBUTIONS TO STRATIGRAPHY

with the Copper Harbor Conglomerate even exist in the areas 

that Mooney and others (1970a, b) call the eastern and western 

basins. If there are none, the definition proposed here may only 

create a problem in areas like the Twin Cities basin that are 

within the midcontinent gravity high.

For geophysical work in parts of the region covered by Lake 

Superior, it might at first appear desirable to place the boundary 

at the top of the main body of lavas rather than higher up, within 

a predominantly sedimentary group of rocks. This would, indeed, 

be true if there were any reason to believe that the Copper Harbor 

Conglomerate remains a predominantly sedimentary formation in 

the central parts of the Lake Superior Basin. Groups of flows 

within the Copper Harbor Conglomerate ("Lake Shore traps"), 

however, pinch out away from the basin axis and become thicker 

and more numerous toward it. This fact suggests that the top of 

the lavas determined seismically is likely to be nearer the top 

than the bottom of the Copper Harbor Conglomerate.

In conclusion, the top of the Copper Harbor Conglomerate 

(base of Nonesuch Shale) appears to be the best stratigraphic 

location for the base of the upper Keweenawan and the Oronto 

Group from both a theoretical and practical standpoint, and a 

purpose of this paper is to propose its adoption (fig. 5). This 

represents a far smaller departure from Irving's original concept 

than do most of the maps and classifications that have attempted 

to follow him more faithfully. Any change in usage such as that 

proposed here is bound to cause some confusion for a while, but 

substituting a contact that can be rigorously and simply defined 

and located over a very large area for one that cannot should, in 

the long run, be a gain.

REFERENCES

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Wisconsin Geol. and Nat. History Survey Bull. 71, 279 p.

Books, K. G., 1968, Magnetization of the lowermost Keweenawan lava flows 

in the Lake Superior area in Geological Survey research 1968: U.S. 

Geol. Survey Prof. Paper 600-D, p. D248-D254.

Butler, B. S., Burbank, W. S., and others, 1929, The copper deposits of 

Michigan: U.S. Geol. Survey Prof. Paper 144, 238 p.

Cornwall, H. R., 1954a, Bedrock geology of the Phoenix quadrangle, Michigan: U.S. Geol. Survey Geol. Quad. Map GQ-34.

 1954b, Bedrock geology of the Delaware quadrangle, Michigan: U.S. 

Geol. Survey Geol. Quad. Map GQ-51.

 1954c, Bedrock geology of the Lake Medora quadrangle, Michigan: 

U.S. Geol. Survey Geol. Quad. Map GQ-52.

 1955, Bedrock geology of the Fort Wilkins quadrangle, Michigan:

U.S. Geol. Survey Geol. Quad. Map GQ-74.
THE BASE OF THE UPPER KEWEENAWAN F21

Cornwall, H. R., and White, W. S., 1955, Bedrock geology of the Manitou

Island quadrangle, Michigan: U.S. Geol. Survey Geol. Quad. Map

GQ-73. 

Cornwall, H. R., and Wright, J. C., 1954, Bedrock geology of the Eagle

Harbor quadrangle, Michigan: U.S. Geol. Survey Geol. Quad. Map

GQ-36. 

 1956a, Geologic map of the Hancock quadrangle, Michigan: U.S.

Geol. Survey Mineral Inv. Field Studies Map MF-46.

1956b, Geologic map of the Laurium quadrangle, Michigan: U.S. Geol.

Survey Mineral Inv. Field Studies Map MF-47. 

Davidson, E. S., Espenshade, G. H., White, W. S., and Wright, J. C., 1955,

Bedrock geology of the Mohawk quadrangle, Michigan: U.S. Geol. Survey

Geol. Quad. Map GQ-54. 

DuBois, P. M., 1962, Paleomagnetization and correlation of Keweenawan

rocks: Canada Geol. Survey Bull. 71, 75 p. 

Gordon, W. C. (assisted by Lane, A. C.), 1907, A geological section from

Bessemer down Black River: Michigan Geol. Survey Rept. for 1906,

p. 397-507. 

Halls, H. C., 1966, A review of the Keweenawan geology of the Lake Superior

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continents: Am. Geophys. Union Geophys. Mon. 10 (Natl. Acad. Sci.-

Natl. Research Council Pub. 1467), p. 3-27.

 1969, Compressional wave velocities of Keweenawan rock specimens 

from the Lake Superior region: Canadian Jour. Earth Sci., v. 6, no. 4, 

pt. 1, p. 555-568.

Halls, H. C., and West, G. F., 1971, A seismic refraction survey in Lake 

Superior: Canadian Jour. Earth Sci., v. 8, p. 610-630.

Hamblin, W. K., 1961, Paleogeographic evolution of the Lake Superior region 

from Late Keweenawan to Late Cambrian time: Geol. Soc. America 

Bull., v. 72, no. 1, p. 1-18.

Hamblin, W. K., and Horner, W. J., 1961, Sources of the Keweenawan conglomerates of northern Michigan: Jour. Geology, v. 69, no. 2, p. 204-211.

Hite, D. M., 1968, Sedimentology of the upper Keweenawan sequence of 

northern Wisconsin and adjacent Michigan: Madison, Wis., Univ. Wisconsin, unpub. Ph.D. thesis, 202 p.

Hubbard, H. A., 1968, Stratigraphic relationships of some Keweenawan rocks 

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Huber, N. K., 1971, The Keweenawan geology of Isle Royale, Michigan: U.S. 

Geol. Survey open-file report, 9 p.

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Survey Mon. 5, 464 p.

Kelley, R. W., comp., 1968, Bedrock of Michigan: Michigan Geol. Survey 

Small Scale Map 2, 1 sheet.

Lane, A. C., 1898, Geological report o,n Isle Royale, Michigan: Michigan 

Geol. Survey, v. 6, pt. 1, 281 p.

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Survey Pub. 6 (Geol. ser. 4), 2 v.: 983 p. 

Lane, A. C., and Seaman, A. E., 1907, Notes on the geological section of

Michigan; Part 1, The pre-Ordovician: Jour. Geology, v. 15, p. 680-695.
F22 CONTRIBUTIONS TO STRATIGRAPHY

Leith, C. K., Lund, R. J., and Leith, Andrew, 1935, Pre-Cambrian rocks of 

the Lake Superior region: U.S. Geol. Survey Prof. Paper 184, 34 p.

Moerlein, G. A., 1963, Structure and stratigraphy of the upper Keweenawan 

rocks in northwestern Wisconsin [abs.]; in Inst. Lake Superior Geology, 

9th Ann., 1963: Duluth, Minn., Univ. Minnesota, Dept. Geology, p. 8.

Mooney, H. M., Craddock, Campbell, Farnham, P. R., Johnson, S. H., and 

Volz, Gary, 1970a, Refraction seismic investigations of the northern 

midcontinent gravity high: Jour. Geophys. Research, v. 75, no. 26, 

p. 5056-5086.

Mooney, H. M., Farnham, P. R., Johnson, S. H., Volz, Gary, and Craddock, 

Campbell, 1970b, Seismic studies over the midcontinent gravity high in 

Minnesota and northwestern Wisconsin: Minnesota Geol. Survey Rept. 

Inv. 11, 191 p.

Ostrom, M. E., 1967, Paleozoic stratigraphic nomenclature for Wisconsin: 

Wisconsin Geol. and Nat. History Survey Inf. Circ. 8, 1 sheet.

Thwaites, F. T., 1912, Sandstones of the Wisconsin coast of Lake Superior: 

Wisconsin Geol. and Nat. History Survey Bull. 25 (Sci. Ser. 8), 117 p.

Tyler, S. A., Marsden, R. W., Grout, F. F., and Thiel, G. A., 1940, Studies 

of the Lake Superior pre-Cambrian by accessory-mineral methods: Geol. 

Soc. America Bull., v. 51, no. 10, p. 1429-1537.

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Keweenawan Series, p. 366-426.]

Vincenz, S. A., and Yaskawa, K., 1968, Phenomenon of partial self-reversal 

in Keweenawan rocks. [Pt.] 2. Magnetization of upper Keweenawan 

lavas and sediments and of lower Keweenawan dikes: Jour. Geophys. 

Research, v. 73, no. 8, p. 2753-2767.

White, W. S., 1952, Imbrication and initial dip in a Keweenawan conglomerate bed [Michigan] : Jour. Sed. Petrology, v. 22, no. 4, p.. 189-199.

 1956, Geologic map of the Chassell quadrangle, Michigan: U.S. Geol. 

Survey Mineral Inv. Field Studies Map MF-43.

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325.

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Duluth, Minn., p. 71-72. 

White, W. S., Cornwall, H. R., and Swanson, R. W., 1953, Bedrock geology

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White, W. S., and Wright, J. C., 1956, Geologic map of the South Range

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Michigan: U.S. Geol. Survey Prof. Paper 400-B, p. B5-B8.

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THE BASE OF THE UPPER KEWEENAWAN F23

Wright, P. E., and Lane, A. C., 1909, Preliminary geological map of the

Porcupine Mountains and vicinity: Michigan Geol. Survey Ann. Rept.

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Contributions to

Stratigraphy,

1971

GEOLOGICAL SURVEY BULLETIN 1354

This volume was published 

as separate chapters A-F
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director
CONTENTS

[Letters designate the separately published chapters]

(A) Changes in stratigraphic nomenclature by the U.S. Geological Survey, 1970. 

by George V. Cohee, Robert G. Bates, and Wilna B. Wright.

(B) Members of the Borden Formation (Mississippian) in north-central Kentucky, by Roy C. Kepferle.

(0) Big Sandy Formation near Wikieup, Mohave County, Arizona, by Richard A. 

Sheppard and Arthur ,T. Gude, 3d.

(D) Revision of stratigraphic names for some Eocene formations in Santa 

Barbara and Ventura Counties, California, by J. G. Vedder.

(E) Age and correlation of the Clinchfield Sand in Georgia, by S. M. Herrick.

(F) The base of the upper Keweenawan, Michigan and Wisconsin, by Walter S. 

White.

U. S. GOVERNMENT PRINTING OFFICE ; 1972 O - 458-352