THE RESUSCITATION OF THE TERM BRYN MAWR GRAVEL. 

By]'. BASCOM . 

. In the course of geologic and physiographic deposits were earlier Pleistocene rather than 

work in eastern Pennsylvania, it has seemed Tertiary. In thus naming these deposits it 

to the writer that the time was ripe for the was the intention to replace by a term 

restriction of the term Brandywine formation, signifying a specific age and stratigraphy 

now including presumably both Pliocene and older terms which included deposits at that 

Pleistocene gravels, and the reinstatement of time recognized to be of different ages. The 

the old term Bryn Mawr gravel for a portion term Brandywine itself, however, has in turn 

of the divided Brandywine. A brief history been found to cover deposits of more than one 

of the nomenclature and usage involved will level and age. 

show the grounds for the choice of terms. In 1920, in the Elkton-Wilmington geologic 

In 1888 the term ''Appomattox" was used folio, 4 theBrandywineformationwasforthefirst 

by McGee 1 for the "older terrace sediments," time separated into early (high-level) and late 

and in 1891, in conference with Hilgard 2 and (low-level) Brandywine. The early Brandyothers, 'McGee correlated these sediments wine gravels are found in the Elkton-Wilwith the deposits of Lafayette County, Miss., mington district at an altitude of 380 feet, 

which had been assigned to the early Quater- capping Egg Hill and other outstanding hills 

nary and which were then called the" Lafayette on the western border of the Elkton quadrangle. 

formation." Since that date the term "Lafay- The late Brandywine gravels lie at altitudes of 

ette" has been very generally used. Recent 220 feet or more. As the firm hard layers 

work, however, has shown that the "Lafayette and decomposed pebbles of the early Brandyformation" of the type locality in the Gulf wine gravels indicate a greater age than the 

region is not Quaternary but of Wilcox Eocene' Pleistocene, they were referred to the Pliocene 

age. A new name was therefore proposed in ( n, and it was stated that the later gravel, 

1915 for the Atlantic coast deposits by Clark,a though provisionally included with the Brandywho called them the Brandywine formation, wine formation, might be of early Pleistocene 

from a type locality in the vicinity of Brandy- age. The deposit at the type locality in 

wine village, Prince Georges County, Md. Maryland is the low-level (200-300 feet) 

The name was defined to cover all the gravels or late Brandywine, presumably of Pleistocene 

that lie above the Sunderland formation at age, as Clark was led to believe; the high-level 

200 feet, in Mafyland reaching an altitude of gravels (390-480 feet) are presumably of 

480 feet and having a width from northwest Pliocene age. Such a time interval between 

to southeast of 40 miles. At that time the the early and late gravels as is now recognized 

Brandywine formation was questionably re- has made it infeasible to treat the deposits as 

ferred to the Pliocene on the ground that it a unit. It is therefore proposed to restrict 

had suffered extensive erosion and that :its the term Brandywine formation to the late or 

constituent minerals showed great decay. lower-level deposits of the type locality, and 

Clark was himself inclined to think that the to reinstate the old term Bryn Mawr gravel 

1 McGee, W J, Three formations of the middle Atlantic slope: Am. 

Jour. Sci., 3d ser., vol. 35, p. 328, 1888. 

2 Hilgard, E. W., Orange sand, Lagrange, and Appomattox: Am. 

Geologist, vol. 8, pp. 128-131, 1891. 

a Clark, W. B., The Brandywine formation of the middle Atlantic 

Coastal Plain: Am. Jour. Sci., 4th ser., vol. 40, p. 499, 1915. 

for the early or high-ievel deposits of Pennsylvania, Delaware, and Maryland (Cecil 

County). 

4 U.S. Geol. Survey Geol. Atlas, Elkton-Wilmington folio (No. 211) 

p. 12, 1920. 

117 
118 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1923-1924. 

The history of the term Bryn Mawr is as 

follows: Carvill Lewis first proposed the .term 

for the deposits of gravel and ironstone 

conglomerate on the "Upland Terrace" of 

eastern Pennsylvania. The report upon these 

gravels, which was made to the Academy of 

Natural Sciences of Philadelphia in November, 

1878, and published in 1880,5 contains the 

following descriptions: 

This hill is easily recognized where uncrossed by 

creeks, being remarkably straight and of uniform 

height. Being the first hill of importance west of the 

Delaware, it often commands a fine view and is a 

favorite site for residences. 

The geographical position of this ancient terrace 

may be more exactly defined in the vicinity of Philadelphia as the hill which crosses Second Street Pike 

near Foxchase * * * and runs north of Kellyville, Clifton, and l\4orton, to Swarthmore College 

and thence past Village Green into Delaware. 

This hill, which is approximately parallel not only 

to the river [Delaware] but also to the shore of the 

Atlantic Ocean and the line of strike of the Cretaceous 

formations of New Jersey, forms, as we have seen, the 

main dividing line between the ancient and the modern 

formations. 

We shall call it for convenience "the Upland 

Terrace." 

A description of .the Pleistocene clays and 

gravels deposited between the "Upland Terrace" 

and Delaware River follows, and then the 

report continues: 

Upon the summits of some of the highest hills in the 

gneissic region back of Philadelphia, at a mean distance of about 9 miles from the river and at elevations 

of from 325 to 450 feet above it, there are isolated 

patches of an ancient gravel, di~erent from any yet 

described, to which we have given the provisional 

name of "the Bryn Mawr gravel." It can always be 

recognized by the presence of sharp or partially 

rounded fragments of a hard, heavy iron sandstone or 

conglomerate. Such fragments are often covered by 

a brownish-black iron glaze. More than ten years ago 

the writer noticEld in the soil of the upper part of 

Germantown pieces of this conglomerate, unlike any 

known rock, and it is only of late that its origin has 

been suspected. It consists of well-rounded pebbles 

of quartzite or siliceous sandstone cemented by iron 

into a stone which is often very hard. This conglomerate is found in occasional fragments upon ground 

over 300 feet high but is not found in abundance until 

an elevation of over 400 feet is reached. At these 

highest points it occurs in a red gravel whose pebbles 

are identical with those of the conglomerate. * * * 

A similar tract of this gravel occurs at Bryn Mawr, 

extending from that place to near Cooperstown. A 

~Lewis, H. C., The surface geology of Philadelphia and vicinity: 

Acad. Nat. Sci. Philadelphia Proc., vol. 32, pp. 258-272, 1880; see also 

pp.zn-~s.~.~aoo. 

good section is exposed in the railroad cut. below the 

station. From this locality, so easy of access from the 

city, we have named the formation. It is here about 

450 feet high and 9 miles from the river. The gravel is 

10 feet deep and lies upon a steeply dipping gneiss so 

completely decomposed that it is as soft as clay. 

At a later meeting (March, 1879) Lewis 

reported that "the Upland Terrace has now 

been .traced continuously from near Trenton, 

through Bucks, Philadelphia, and Delaware 

counties to beyond Wilmington in Delaware.'' 

He calls attention to 

the great development of the Bryn Mawr gravel in 

Delaware, and to the indications of its assuming an 

important position in the geology of the Southern 

States. * * * Numerous hills in Delaware County 

have been found to be capped by this formation, and in 

northern Delaware it covers the gneissic hills in patches 

several miles long and comes close to the river. * * * 

This formation so abundant in Delaware is thus proved 

to be by no means a local one, and it is probable that 

it will be identified with some of the formations grouped 

together under the name of "Southern drift." 6 

It is plain from this account that by the 

"Upland Terrace" was meant the up~and the 

lowest slopes of which are at the 300-foot level, 

separated by an escarpment from the lower terrace upon which lie the low-levelBrandywine deposits and rising to the northwest to the 480-foot 

level, with a dominating level of 400 feet; 

and that by the term Bryn Mawr gravel was 

meant the gravel and ironstone conglomerate 

capping the interstream areas of this terrace. 

The gravels of ·the type localities described 

by Lewis are plainly the high-level or early 

Brandywine gravels, and the term Bryn Mawr 

as used by Lewis covered only the high-level 

Brandywine deposits as they occur in Pennsylvania and Delaware. The term received 

considerable usage prior to the introduction 

of the designation "Lafayette." The Second 

Pennsylvania Geological Survey referred to 

the Bryn Mawr gravel as Tertiary or Upper 

Cretaceous. McGee at first regarded it as of 

Columbia age and later classified it as lower 

Potomac. 

The term Bryn Mawr gravel is here proposed for the high-level Brandywine because 

it has the claim of priority, preceding in usage 

all other designations for the Tertiary deposits 

of the Atlantic slope, because the gravels of the 

type locality are the older gravels, and because 

s Op. cit., pp. 277-278. 
THE RESUSCITATION OF THE TERM BRYN MAWR GRAVEL. 119 

the 400-foot terrace, upon ;which the early 

Brandywine deposits lie, is. so prominent a 

physiographic feature in eastern Pennyslvania, 

where these gravels and terraces were so early 

described and given a local name. 

The correlation of the Bryn Mawr formation 

with other Tertiary gravels near the fall line 

depends upon the origin of the gravels and upon 

their topography. Whatever origin is eventually ascribed to the high-level Brandywine by 

those at work on the Tertiary and Pleistocene 

deposits of the Atlantic coast, it will doubtless 

be required to explain acceptably all the highlevel gravels, so similar are these deposits and 

so uniform are the levels upon which they are 

found. 

That these high-level gravels were originally 

deposited in detached areas is quite possible, 

but their approximate equivalence is so little 

to be doubted that until it is disproved the less 

misleading and less cumbersome method would 

seem to consist in the use of a single term. The 

logical alternative is to give a separate name 

to every patch of gravel above the low-level 

or typical Brandywine-that is, above the 

300-foot level-an alternative which would 

lead to confusion and which would not reflect 

the present state of our knowledge. 

J