Clays Ferry Formation 

(Ordovician) 

A New Map Unit in 

South-Central Kentucky

By GORDON W. WEIR and ROBERT C. GREENE

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1224-B

Prepared in cooperation with the 

Kentucky Geological Survey .
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

U.S. GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965

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

Washington, D.C. 20402 - Price 15 cents (paper cover)
CONTENTS

Page

Abstract_______________________________________________________ Bl

Introduction._____________________________________________________ 1

Previous nomenclature.____________________________________________ 2

Lithology__ __._______-_____--__-_______._-_____-_-.___________._ 7

Outcrop.._________----____-_-_________--_---------__-__--_-__-.__ 8

Contacts.__-__--___---__-___---_-___--__----__-----------_-______ 11

Fossils _--_-___-__-_--------------------_-----------------------_- 1.1

Thickness and extent._--_______---_--_______-______-_-_._____.__._ 11

Age and correlation__________-_____--__-.__-___---_-_____-____-.____ 13

Type section._____________________________________________________ 14

References_ _____________________________________________________ 17

ILLUSTRATIONS

Page

FIGURE 1. Index map of central Kentucky.__________________________ B2

2. Sketch map of Clays Ferry crossing______________________ 3

3. Nomenclature chart_-__-__-______-__--_________._________ 4

4. Nomenclature sections.__--__---__---__-______-_-_--_____ 5

5. Photograph of lowest zone of abundant Sowerbyella.. ________ 6

6. Photograph of base of Clays Ferry Formation_____________ 9

7. Photograph of top of Clays Ferry Formation_____________ 10

TABLES

Page 

TABLE 1. Fossils from the Clays Ferry Formation___________________ B12

2. Source of fossils collected from Clays Ferry Formation______ 13

in

CONTRIBUTIONS TO STRATIGRAPHY

CLAYS FERRY FORMATION (ORDOVIGIAN) A NEW MAP 

UNIT IN SOUTH-CENTRAL KENTUCKY

By GORDON W. WEIR and EGBERT C. GREENE

ABSTRACT

The Clays Ferry Formation is a newly recognized major rock-stratigraphic 

unit in south-central Kentucky. It includes strata that were previously divided 

on the basis of the fauna into (in ascending order) the Cynthiana Formation of 

A. F. Foerste, the Fulton Shale, and the Million Shale of J. M. Nickles as used 

by A. F. Foerste. The Clays Ferry consists of interstratified thin-bedded shale, 

limestone, and siltstone. It ranges from about 120 to 220 feet in thickness, and 

is of late Middle and early Late Ordovician age. The Clays Ferry Formation 

overlies and intertongues with thick-bedded limestone of the Lexington Limestone ; it grades into the overlying Garrard Siltstone.

INTRODUCTION

The name Clays Ferry Formation is here given to a mappable unit 

of interbedded shale, limestone, and siltstone that crops out in southcentral Kentucky. The Clays Ferry Formation overlies thick-bedded 

granular limestone of the Lexington Limestone as defined by Black 

and others (1965). It is overlain by the Garrard Siltstone. The type 

locality (figs. 1 and 2) is on the south side of the Kentucky River in 

Madison County across the river from the settlement of Clays Ferry, 

Fayette County, Ky. The type section (p. B14) is exposed in a gully a 

few tens of feet northeast of the eastern span of the Interstate Highway 75 bridge over the Kentucky River at Clays Ferry and in roadcuts 

on the northeast side of the highway in the southern part of the Ford 

quadrangle, Kentucky.

This report is based in large part on the geological mapping of 

Kentucky being conducted by the U.S. Geological Survey in cooperation with the Kentucky Geological Survey. Areas not currently 

being mapped were studied chiefly in the spring and summer of 1963. 

The writers are indebted to D. F. B. Black, E. R. Cressman, and G. C. 

Simmons for information concerning the stratigraphy of the Clays 

Ferry Formation. R. J. Ross, Jr., helped collect fossils at the type 

locality.

Bl
B2 CONTRIBUTIONS TO STRATIGRAPHY

LEXINGTON

Mount Sterling

o Winchester 

E

0 Richmond 

VALLEY VIEW 

QUADRANGLE

Harrodsburg

10 10 20 MILES

SECTIONS 

A. Sledd Branch

B. Clays Ferry (Type section of Clays Ferry Formation) 

C. Boonesboro Beach West 

C". Boonesboro Beach 

D. Fourmile Creek 

E. Logan Lick Road

,A-;

Location of area

FIGURE 1. Map of central Kentucky showing location of type section and representative sections of the Clays Ferry Formation shown in figure 4.

Campbell (1898) included the rocks of the Clays Ferry Formation 

in the Winchester Limestone (fig. 3), which he described from outcrops near the town of Winchester, Ky. Near this town the Winchester Limestone of Campbell (1898) is divisible into two lithologic 

units: a lower unit of thick-bedded granular limestone with seams of 

shale, and an upper unit of limy shale interstratified with thin-bedded 

aphanitic and granular limestone and minor thin-bedded limy siltstone. Southwestward from Winchester, the lower unit thins and 

probably intertongues with the upper unit, so south of the Kentucky 

Kiver the Winchester Limestone of Campbell (1898) is characterized 

by much shale. The name Winchester was later restricted by Miller 

(1905, p. 9, 22-23) to the lower part of the Winchester Limestone of 

Campbell (1898), and Winchester was used in this restricted sense by 

Nickles (1905) and Matson (1909).

To approximately the same unit named Winchester by Miller 

(1905), Foerste (1906, p. 10, 13, 14, 211) gave the name Cynthiana 

Formation, from the town of Cynthiana about 25 miles northeast of
CLAYS FERRY FORMATION, SOUTH-CENTRAL KENTUCKY B3

4 /Line of section; chevrons point 

lj stratigraphically upward

FIGURE 2. Map of the Clays Ferry crossing of the Kentucky River showing 

location of the type section of Clays Ferry Formation.

Lexington, Ky. Since Foerste proposed Cynthiana, the name Winchester has been little used. The Cynthiana Formation was redefined 

by Hall and Palmquist (1960) to include beds below those that made 

up Foerste's (1906) Cynthiana (see fig. 3). The Cynthiana was so 

recognized by the Geological Survey until the name was abandoned 

(Black and others, 1965).

For the beds of the Eden Group overlying the Winchester of Miller 

(1905) and underlying the Garrard Siltstone, Nickles (1905, p. 15, 

25-26) proposed the name Million Shale, after the village of Million, 

5 miles northeast of Richmond. The Million was distinguished by its 

shaly character and by the presence in its lower layers of the bryozoan 

"Calloporasigillarioides" (=? Hallopora onealli sigillarioides) and 

by the abundant brachiopod "Plectarribonites sericeus" (=/Sowerbyella rugosa). North of the Kentucky River the lowest zone of 

abundant Sowerbyella generally is only a few feet to about 20 feet
OVERLYING UNIT 

(details omitted)

APPROXIMATE

EQUIVALENT

OF CLAYS

FORMATION

NEAR CLAYS

FERRY

UNDERLYING UNIT 

(details omitted)

Campbell (1898)

Garrard 

sandstone

Winchester

Lexington 

limestone

Miller (1905)

1

 o

Garrard 

substage

-

Winchester 

substage

Bigby 

substage

Nickles (1905)

en group

Garrard 

sandstone

Million

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Winchester 

group

Lexington 

group

Foerste (1906)

.2

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ana Fm

Paint Lick 

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Million

Fulton

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Point Pleasant 

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Greendale 

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Lexington 

Formation

Matson (1909

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Winchester 

limestone

Lexington 

imestone

McFar 

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Fr

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an (1938, 1943) 

cFarlan and 

eeman (1935)

Garrard

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Million

Fulton

Rogers Gap

Bromley

Woodburn limestone 

of 

Lexington limestone

McFarlan (1954)

Garrard

siltstone

Million

shale

Fulton shale

Cynthiana 

limestone 

Woodburn limestone 

; of 

Lexington limestone

* 

McFarlan and 

Campbell (1955)

=

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Garrard

siltstone

Cynthiana

Woodburn of 

Lexington

Hall*and 

Palmquist 

(1960)

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Member

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and Hall 

(1961)

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(1905) 

used b

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(1906)

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/ Rogers G

Mbr as use

Foerste (1

Greendale 

\ (1906

Woodbu

Limestone

FIGURE 3. Nomenclature previously applied to stratigraphic units expos

Formation. Asterisks indicate reports with geologic map or descripti

Ferry Formation.
CLAYS FERRY FORMATION, SOUTH-CENTRAL KENTUCKY B5

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B6 CONTRIBUTIONS TO STRATIGRAPHY

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FIGTJEE 5. Lowest zone of abundant Sowerbyella (at pick handle) in interstratifled shale and thin-bedded limestone at type section of Clays Ferry Formation, 

roadcuts on northeast side of Interstate Highway 75 about 500 feet southeast 

of bridge over Kentucky River. This zone is the base of the Million Shale of 

Nickles (1905) and is about 100 feet above the base of the Clays Ferry 

Formation shown in figure 6.
CLAYS FERRY FORMATION, SOUTH-CENTRAL KENTUCKY B7

above the lithologic break between granular limestone below and the 

interbedded shale and limestone above. However, near Million, the 

presumed type locality of the formation, and elsewhere south of the 

Kentucky Kiver the lowest zone of abundant Sowerbyella is about 

100 feet above the lithologic break (figs. 4 and 5). The paleontologic 

criteria for distinguishing the Million Shale of Nickles (1905) were 

used by Foerste (1906) and all later stratigraphers.

Foerste (1906) recognized the Fulton, the zone of Triarthrus becki, 

as a layer as much as 3 feet thick at the base of the Million Shale of 

Nickles (1905) in central Kentucky. Later workers who recognized 

the Fulton Shale considered it to be the basal formation of the Eden 

Group and to be a faunal unit characterized by abundant columnals 

of Merocrinus cwtus (McFarlan and Freeman, 1935, p. 2001; McFarlan,1943,p.24).

Some geologists considered the rocks between the Cynthiana and 

the Garrard to be the Eden Shale or an unnamed unit of the Eden 

Group (fig. 3). All geologists, however, apparently placed the upper 

contact of the Cynthiana Formation just below the lowest bed of 

abundant Sowerbyella or abundant Merocrinus. In much of southcentral Kentucky these beds are about 100 feet above the change from 

granular limestone to interbedded shale and limestone, and are near 

the middle of the mappable lithologic unit (fig. 5).

In summary, the interbedded shale, limestone, and siltstone of the 

mappable rock-stratigraphic unit that is well exposed near Clays Ferry 

have in the past been assigned to the Winchester Limestone of Campbell (1898), or to the Winchester as restricted by Miller (1905), or to 

the Cynthiana Formation of Foerste (1906), and to an unnamed division of the Eden Group or to the Fulton Shale and Million Shale 

of Nickles (1905) as used by Foerste (1906). The name Winchester 

has, for all practical purposes, been abandoned. The Cynthiana Formation, the Fulton Shale, and the Million Shale of Nickles (1905) are 

f aunally defined units that do not include all the Clays Ferry Formation. None of these old names can now be used without major changes 

of their definitions and consequent further confusion of the nomenclature. The rock-stratigraphic unit described in this report, therefore, is given a new name the Clays Ferry Formation.

LITHOLOGY

The Clays Ferry Formation consists of limestone, shale, and siltstone. Limestone and shale are irregularly interbedded throughout 

the formation, and locally either may be dominant. The Clays Ferry 

as a whole, however, is characterized by its shale content, which is 

much greater than in underlying and overlying formations. Siltstone
B8 CONTRIBUTIONS TO STRATIGRAPHY

is a minor constituent but is common to abundant in the upper onequarter of the formation. The proportions of limestone, shale, and 

siltstone differ from place to place (fig. 4), and few beds or sets of beds 

are traceable for more than several hundred feet.

Thin beds are characteristic of the Clays Ferry Formation (figs. 5, 

6, and 7). Most beds are only a few inches thick; few are more than 

a foot thick.

Limestone is the most conspicuous rock in the Clays Ferry and 

makes up about 30 to 60 percent of the formation. The limestone is 

commonly light to dark gray and weathers gray or yellowish brown. 

It ranges from micrograined to very coarse grained but is mostly 

fine to medium grained. Limestones of different grain size are closely 

interbedded and in places intergrade. Fossils, chiefly brachiopods 

and bryozoans, are common in most beds of the limestone. Some 

coarse-grained layers are composed largely of brachiopod shells, but 

micrograined 'beds are barren or sparsely fossiliferous. The limestone is mostly in even beds 1 to 6 inches thick. Sparse thicker beds, 

as much as 3 feet thick, are generally lenticular, and some are 

contorted.

Shale makes up about 30 to 60 percent of the Clays Ferry Formation, but because of its poor exposure the percentage of shale in the 

formation is commonly difficult to measure. Most shale is dark greenish gray or olive gray and weathers yellowish gray or yellowish 

brown. Some shale is silty and limy, and locally grades into siltstone 

and limestone. Most shale is distinctly laminated in sets 1 to 12 inches 

thick. Fossils are generally sparse, though small bryozoans are 

locally common.

Siltstone makes up about 5 to 15 percent of the Clays Ferry and is 

mostly in the upper part of the formation. Where fresh, the rock 

is limy, greenish gray, and well indurated; where weathered and 

leached, it is yellowish brown, friable, and punky. Most siltstone is 

in even 'beds 1 to 3 inches thick. 'Some thicker units, as much as 3 

feet thick, are contorted lenses that weather to form knobby outcrops. 

Fossils are sparse in the siltstone except where it is very limy or grades 

to limestone. Siltstone of the Clays Ferry resembles that of the overlying Garrard Siltstone but is more thinly bedded.

OUTCROP

Because of its shale content, the Clays Ferry Formation generally 

is poorly exposed. It is less resistant than underlying and overlying 

formations and commonly forms moderate slopes littered with plates 

and thin slabs of limestone.
CLAYS FERRY FORMATION, SOUTH-CENTRAL KENTUCKY B9
BIO CONTRIBUTIONS TO STRATIGRAPHY

«i^£

jfcj^v',.^* -\

SOdfK: < > - i

FIGURE 7. Upper contact of Clays Ferry Formation (about 1 ft below pick) 

at type section of Clays Ferry Formation in roadcut on northeast side of 

Interstate Highway 75 about 1,000 feet southeast of bridge over Kentucky 

River. Overlying unit is Garrard Siltstone. Basal unit of Garrard (at pick) 

is contorted, resulting in steep dips and local discordance at the contact.
CLAYS FERRY FORMATION, SOUTH-CENTRAL KENTUCKY Bll

CONTACTS

The Clays Ferry Formation overlies thick-bedded granular limestone of the Lexington Limestone in south-central Kentucky (Black 

and others, 1965). The basal contact of the Clays Ferry is fairly 

sharp at the type locality (fig. 6). East of the type locality, the base 

of the Clays Ferry is transitional through a few feet to a few tens of 

feet; the contact is placed so as to exclude thick-bedded granular 

limestone and to include, in the Clays Ferry, thin-bedded limestone, 

micrograined limestone, and persistent shale units.

The Clays Ferry Formation grades into the overlying Garrard 

Siltstone, which consists of thick beds of limy siltstone and sparse thin 

lentils of shale and limestone. Beds of siltstone are thicker and more 

abundant near the 'top of the Clays Ferry Formation, and beds of 

limestone and shale are less abundant. The upper contact is placed 

at the top of the highest relatively persistent bed of limestone in the 

Clays Ferry Formation. Locally, the basal bed of the Garrard Siltstone is thick and contorted into bulbous lenses with crumpled internal 

layers. At such localities (fig. 7) the contact is sharp and appears 

discordant, though it may lose this character as the basal bed of the 

Garrard thins.

FOSSILS

Table 1 shows the megafossil fauna of the Clays Ferry Formation 

at the type locality. The most conspicuous element of this fauna is 

the large flat brachiopod Rafinesqwna.

Fossil collections of other sections of the Clays Ferry Formation 

are incomplete or not yet studied. The faunas listed by McFarlan 

and Freeman (1935) for units they called the Rogers Gap and Fulton 

Formations at localities south of the Kentucky River- are from beds 

that are here included in the Clays Ferry Formation.

THICKNESS AND EXTENT

The Clays Ferry Formation is 190 feet thick at its type section. It 

ranges from about 120 feet thick near Winchester to about 220 feet 

in the western part of the Valley View quadrangle. North and east 

of the type locality the formation thins markedly within less than 10 

miles (fig. 4), as the lower part of the Clays Ferry grades into and 

intertongues with the upper part of the Lexington Limestone (Black 

and others, 1965).

The Clays Ferry Formation crops out widely in south-central Kentucky. The formation has been mapped in the Valley View quadrangle 

and adjacent quadrangles, and it has been recognized in many sections 

between Richmond, Harrodsburg, Lexington, and Mount Sterling. 

Determination of its northern and western extent requires further 

field study.
B12 CONTRIBUTIONS TO STRATIGRAPHY

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CLAYS FERRY FORMATION, SOUTH-CENTRAL KENTUCKY B13

TABLE 2 Source of fossils collected from Clays Ferry Formation

[Collins D1168-CO through D1181-CO made from Clays Ferry! Formation exposed in 

readouts 500 to 2,000 ft. west of the type section along the Old Clays Ferry Road. 

Collins D1182-'CO through D11V1-CO and D1195-CO made from the type section of the 

Clays Ferry Formation in roadcuts along Interstate Highway 75 from 20 to 1,000 ft 

southeast of the 1-75 bridge over the Kentucky River at Clays Ferry. Asterisk indicates float; all other samples are from outcrop]

Height above base of Height above base of 

Clays Ferry Formation Clays Ferry Formation 

USGS colln. No. (feet) US&S colln. No. (feet)

D1168-CO - ___ 6 mi si -no 97

1169-CO __________

1170-CO _________

1171-CO __ __-__

'1172-CO'- _ '- 

1173-CO ________

1174-CO ___ _

1175-CO _________

1176-eO __________

1178-CO* _____ __

1177-CO __________

1179-CO ___ _

1180-CO* ______

_____ 8

_______ 10

 ___ 15

__ ____ 24

30

_____ 37

_____ 38

_____ 46

____ 55-60

_____ 60

_ ____ 71-75

. ____ 75

1195-CO

1182-CO __ _______

1183-CO __ .

1 -I QA _ flfl

1185-CO ___ .

1186-CO _- _ .

1187-CO* -

1189-dO ___ -

1188-00 ________

1190-CO _____ _

1191-CO __ _ _

. _____ 101

. _____ 120

. ____ . . 124

. _____ 125

. _____ 130

. _____ 159

 __ 159

. _ __ 165

. __ __ 171

. _____ 182

. _____ 187-190

AGE AND CORRELATION

The Clays Ferry Formation south of the Kentucky Kiver is probably of late Middle Ordovician and early Late Ordovician age. It 

is mostly of Late Ordovician age near Lexington and Winchester 

where the formation is thinner because of intertonguing of its lower 

part with the Lexington Limestone (Black and others, 1965). The 

underlying.Lexington Limestone is Middle Ordovician in age (Black 

and others, 1965), and the overlying Garrard Siltstone is Late Ordovician (Hall and Palmquist, 1960). McFarlan and Freeman (1935, 

p. 1986-1992,2001) placed the boundary between the "Trenton" (Middle Ordovician) and "Eden" (Upper Ordovician) in fossiliferous 

strata that are near the middle of the Clays Ferry Formation at the 

type locality and elsewhere south of the Kentucky River. Because of 

lithologic changes northward, these fossiliferous strata are near the 

base of the Clays Ferry Formation near Lexington and Winchester.

The age assignments and previously identified f aunal units suggest 

that the Clays Ferry Formation of south-central Kentucky correlates 

with all or part of the Latonia Shale, the Fulton Shale, and the upper 

part of the Cynthiana Formation, as these terms were used in northern 

Kentucky by Palmquist and Hall (1961).
B14 CONTRIBUTIONS TO STRATIGRAPHY

TYPE SECTION

Type section of the Clays Ferry Formation

[Section begins about 45 ft above old Clays Ferry Road, a few tens of feet northeast of 

eastern span of Interstate Highway 75 in unnamed gully, continues southeastward up

to highway level and thence about 1,000 southeastward along northbound lanes of the

highway In southern part of Ford quadrangle, Madison County, Ky.]

Garrard Siltstone: Th(fe )8* 

Siltstone, greenish-gray (5(rY 7/1) a ; weathers slightly darker; limy, 

in even beds a few inches to several feet thick, but most thick beds 

in flow rolls, contorted lenses with crumpled internal layers. Limestone is light gray, medium to coarse grained; in sparse discontinuous thin lentils, 1 to 3 in. thick; abundant flat brachiopods. Basal 

contact of Garrard is sharp and distinct on east side of highway 

at highway level, where contorted beds mark the base, but contact on 

west side of highway is gradational and less distinct where basal 

siltstone is more thinly and evenly bedded_________ __ 31

Total Garrard Siltstone_________________________ 31

Olays Ferry Formation:

Shale (50 percent), siltstone (25 percent), and limestone (25 percent). Shale is dark greenish gray (5GY 4/1), slightly silty to 

silty; in laminae 2 to 3 mm. thick, grouped in sets 1 to 12 in. thick; 

sparse bryozoans. Siltstone is dark greenish gray (5GT 4/1) to 

greenish gray (5GY 7/1) ; limy and locally grades to silty limestone ; interstratifled irregularly throughout unit but dominant near 

top, in even beds 1 to 3 in. thick; sparse brachiopods. Limestone is 

medium light gray (#6), light olive gray (5T 6/1), and medium 

gray (N5), mostly poorly sorted, chiefly very fine to coarse grained; 

disseminated grains and flakes of silt and common fine to coarse 

fossil fragments mostly in gently wavy beds 1 to 8 in. thick; also 

fine grained in fairly even beds, 1 to 6 in. thick, and very fine 

grained, well sorted in beds less than 1 in. thick and in lenticles 1 to 

2 in. long in shale. Fossils, sparse to very abundant, chiefly brachiopods, gastropods, and bryozoans; less abundant are pelecypod and 

trilobite fragments. Thickness approximate because of variation in 

upper contact.

The following fossil collections were made from this unit: 

D1186-CO, 20 ft above base of unit; D1187-CO, float, 20 ft above 

base; D1189-CO, 25 ft below top; D1188-CO, 32 ft above base; 

D1190-CO, 8 ft below top, D1191-CO, 0 to 3 ft below top ______ 51

1 Color names with numbers based on color chart by Goddard and others (1948).
CLAYS FERRY FORMATION, SOUTH-CENTRAL KENTUCKY B15

Type section of the Clays Ferry Formation Continued

Thickness 

Clays Ferry Formation Continued (feet)

Shale (50 percent), limestone (30 percent), and siltstone (20) percent). Generally similar to overlying unit but contains less siltstone. Limestone is dominantly medium to coarse grained, in beds 

1 to 6 in. thick interstratifled with equal or greater thicknesses of 

shale and siltstone; a few intervals about 5 to 10 ft thick are 50 

to 70 percent limestone. Whole and broken large flat brachiopods 

abundant in coarse-grained limestone; other fossils sparse. Top 

arbitrarily placed at top of shale 'bed below steepening of slope, 

which probably reflects upward increase in percentage of siltstone. 

The following fossil collections were made from this unit: 

D1182-CO, 1 ft above base of unit; D1183-CO, 5 ft above base, 

D1184-OO, 6 ft above 'base; D1185-CO, 11 ft above base ______ 20

Siltstone, greenish-gray (5GY 6/1), limy, admixed with 10 to 20 percent silty, medium- to coarse-grained limestone J in prominent bed; 

pinches and swells along strike but persistent; ranges from about 

1 to 3 ft in thickness; partly contorted into flow rolls; weathers to 

form rounded protuberances. Brachiopods abundant and bryozoans 

common in limestone; siltstone mostly barren but contains sparse 

brachiopods adjacent to fossiliferous limestone lenses -___ 2

Shale (50 percent), limestone (35 percent), and siltstone (15 percent). 

Similar to overlying interbedded shale, limestone, and siltstone. 

About 7 ft above base is silty, coarse-grained limestone aibouit 1 ft 

thick that contains abundant small brachiopods, Sowerbyella; fossil colln. D1195-CO made from this bed; shale grades to limestone 

and siltstone about 100 ft farther south. Sowerbyella also abundant in limestone bed at top of unit. Note:' Lowest bed with 

Sowerbyella in profusion is approximately the base of the Million 

Shale of Nickles (1905) ; see McFarlan and Freeman (1935) and 

McFarlan (1943, p. 24)_________________________ 23.5

Limestone (50 percent), shale (45 percent), and siltstone (5 percent). 

Generally similar to units described above; chief differences are 

percentages of rock types; lowest unit with significant amount of 

siltstone. Limestone contains common to abundant medium to very 

coarse fossil fragments and sparse whole large flat brachiopods. 

Siltstone is dark greenish gray (5GY 4/1) ; very limy and in part 

grading to silty, very fine grained limestone; in contorted bed 4 to 

10 in. thick at top of unit and in beds about 1 in. thick interstratified 

with shale and limestone__________________ 13

Limestone (70 percent) and shale (30 percent). Limestone is light 

gray (#7) to medium light gray (N6) ; weathers about same with 

brownish tint; fine to medium grained; mostly in gnarly, roughsurfaced beds 1 to 4 in. thick and in discontinuous lenticles a few 

inches to a few feet long with irregular wavy silty shale partings 

and seams as much as 2 in. thick. Abundant jumbled large brachiopods and sparse crinoid columnals. Top of unit marked by bed of 

limestone about 2 ft thick; highest conspicuous thick bed of 

limestone in section; along strike this bed thins and is vague. 

Shale, dominantly greenish gray (5#Y 6/1), similar to that 

described above____ ___ ___ _ 3
B16 CONTRIBUTIONS TO STRATIGRAPHY

Type section of the Clays Ferry Formation Continued Thickness 

Clays Ferry Formation Continued (feet)

Mostly covered; a few poor outcrops suggest that this interval is shale 

and limestone similar to underlying unit. Limestone is light 

brownish gray (SYR 6/1), poorly sorted, micrograined to coarse 

grained; cririoidal in wavy bed a'bout 6 in. thick; crinoid columnals, 

%2 to % in. in diameter, very abundant; sparse fragments of small 

brachiopods and bryozoans; also limestone, very fine grained in even 

bed, 3 in. thick, containing brachiopods, 'bryozoans and fragments 

of trilobites, and very sparse crinoid columnals. Top of unit 

approximately level with highway at bridge 11

Shale (60 percent) and limestone (40 percent). Shale is grayish 

yellow (SY 8/4) and yellowish gray (57 8/1) ; clayey, in part 

limy; laminated in sets 1 to 12 in. thick and locally contains a few 

lenticles of limestone; interbedded with limestone; bryozoans 

sparse to common. Limestone is light brownish gray (SYR 6/1) ; 

weathers same and yellowish gray; fine to coarse grained and 

silty; poorly sorted; in irregular lensing beds % to 4 in. thick; 

irregularly interstratified with shale; fragmental and whole flat 

brachiopods abundant, bryozoans common to abundant, and gastropods common in bed about 5 ft above base; small crinoid columnals 

common to abundant in upper part of unit ____ _ 10

Limestone (70 percent) and shale (30 percent). Limestone is chiefly 

yellowish gray (SYR 6/1), in part light brownish gray (SYR 6/1) 

and medium gray (#5), chiefly poorly sorted, silty, fine to medium 

grained but in part coarse grained and in part fairly sorted, silty, 

very fine grained; chiefly in rough beds about 8 to 12 in. thick; 

lower part of unit has flow rolls of silty very fine grained limestone, 

contorted lenses 5 to 20 in. thick with obscure internal layering 

but in part with crumpled laminae; flat brachiopods abundant 

and jumbled in many beds; cylindrical bryozoans common,.gastropods sparse. Shale similar to shale in overlying unit. Top of 

unit marked by limestone with much reddish-weathering phosphatic(?) granular material; base marked by flow roll 6 to 14 in. 

thick of laminated very fine grained limestone_________ __ 26. 5

Shale (65 percent) and limestone (35 percent). Shale is similar to 

shale in overlying unit. Limestone is yellowish gray (SYR 6/1) ; 

well sorted in individual beds; chiefly fine and medium grained, in 

part silty, very fine grained and in part coarse grained with streaks 

and flakes of limy siltstone; in even and mildly contorted beds % to 

8 in. thick and in discontinuous lenticles as much as 2 in. thick. 

Fossils common to abundant in most beds of limestone but generally 

very sparse within even beds of silty micrograined limestone; flat 

brachiopods and cylindrical bryozoans abundant, gastropods and 

trilobite fragments sparse to common. Some silty fine-grained limestone grades to limy fossiliferous shale. Limestone more abundant 

in upper part of the unit; percentage of limestone and shale are 

about equal at top_____________________________ 30

Total Clays Ferry Formation ___________________ 190
CLAYS FERRY FORMATION, SOUTH-CENTRAL KENTUCKY B17

Type section of the Clays Ferry Formation Continued

Thickness

Lexington Limestone (incomplete) : (feet) 

Limestone, light-brownish-gray (5Y 6/1), weathering medium-lightgray (#6), medium to very coarse grained, fossils fragmental. In 

part is in planar sets of crossbeds; in part is horizontally bedded 

with wavy bedding planes; some bedding planes marked by silty and 

shaly partings and seams, which are emphasized by reddish iron 

stain. Fossil fragments abundant, chiefly large cylindrical bryozoans and brachiopods; whole fossils very sparse; patches of 

bryozoans give spotty appearance to some beds. Patches of irregularly crystallized white calcite locally conspicuous. Upper part 

contains common to abundant brownish-, reddish-weathering interstitial phosphatic material _ 83

NOTE. Arbitrary base of section, not base of exposure; underlying the medium- to coarse-grained partly crossbedded limestone 

described above is about 30 ft of limy shale interstratifled with 

fine-grained limestone, commonly in contorted beds; below this is 

about 50 ft of unevenly bedded fine- to medium-grained fossiliferous 

limestone; base of local exposure is at Kentucky River fault about 

500 ft southwest of old Clays Ferry bridge.

REFERENCES

Black, D. F. B., Cressman, B. R., and MacQuown, W. 0., Jr., 1965, The Lexington 

Limestone (Middle Ordovician) of central Kentucky: U.S. Qeol. Survey Bull. 

1224-0. (In press.)

Campbell, M. R., 1898, Description of the Richmond quadrangle [Kentucky]: 

U.S. Geol. Survey Geol. Atlas, Folio 46, 4 p., 4 maps (scale, 1:125,000).

Foerste, A. F., 1906, The Silurian, Devonian, and Irvine formations of eastcentral Kentucky, with an account of their clays and limestones: Kentucky 

Geol. Survey Bull. 7, 369 p., 10 figs., 8 pis.

 1914, The Rogers Gap fauna of central Kentucky: Cincinnati Soc. Nat.

History Jour., v. 21, p. 109-156. 

Goddard, E. N., chm., and others, 1948, Rock-color chart: Washington, Natl.

Research Council (repub. by Geol. Soc. America, 1951), 6 p. 

Hall, F. R., and Palmquist, W. N., Jr., 1960, Availability of ground water in

Clark, Estill, Madison, and Powell Counties, Kentucky: U.S. Geol. Survey

Hydrol. Inv. Atlas HA-19.

Jillson, W. R., 1929, Geologic map of Kentucky: Kentucky Geol. Survey, ser. 6. 

McFarlan, A. C., 1938, Stratigraphic relationships of Lexington, Perryville, and

Cynthiana (Trenton) rocks of central Kentucky: Geol. Soc. America Bull.,

v. 49, p. 989-996.

 1943, Geology of Kentucky: Lexington, Ky., Univ. Kentucky, 531 p., 

117 pis., 42 figs.

 1954, Central Kentucky [column in correlation chart] in Twenhofel, W. H.,

chm., and others; Correlation of the Ordovician formations of North America 

Geol. Soc. America Bull., v. 65, pi. 1 (facing p. 298).

McFarlan, A. C., and Campbell, L. J., 1955, Geological itinerary Kentucky 

highways, in Russell, R. J., ed., Guides to southeastern geology, prepared 

for the 1955 ann. mtg. of the Geol. Soc. America and associated societies: 

New York, Geol. Soc. America, p. 100-194, 51 figs.
B18 CONTRIBUTIONS TO STRATIGRAPHY

McFarlan, A. G., and Freeman, L. B., 1935, Rogers Gap and Fulton formations 

in central Kentucky: Geol. Soc. America Bull., v. 46, p. 1975-2006, 3 pis., 

2 figs.

McFarlan, A. C., and Goodwin, S. S., 1930, Areal geologic map of Madison 

County, Kentucky: Kentucky Geol. Survey, ser. 6 (scale, 1:63,360).

Matson, G. C., 1909, Water resources of the Blue Grass region, Kentucky: U. S. 

Geol. Survey Water-Supply Paper 233,223 p., 6 figs., 3 pis.

Miller, A. M., 1905, The lead and zinc-bearing rocks of central Kentucky with 

notes on the mineral veins: Kentucky Geol. Survey Bull. 2, 35 p., 13 photographs, map of Highbridge and Trenton area showing location of mineral 

veins (scale, 1: 300,000).

 1915, The Ordovician Cynthiana formation: Am. Jour. Sci., ser. 4, v. 

40, p. 651-657.

 1919, The geology of Kentucky: Kentucky Dept. Geology and Forestry,

ser. 5, Bull. 2,392 p.

Nickles, J. M., 1905, The Upper Ordovician rocks of Kentucky and their 

Bryozoa: Kentucky Geol. Survey Bull. 5, 64 p., 3 pis.

Palmquist, W. N., Jr., and Hall, F. R., 1961, Reconnaissance of ground-water 

resources in the Blue Grass region, Kentucky: U.S. Geol. Survey WaterSupply Paper 1533, 39 p.

Templeton, J. S., and Willman, H. B., 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geol. Survey Bull. 89, 260 p., 41 figs.

O