MARYLAND GEOLOGICAL SURVEY 79 



The Lafayette Formation. 1 



The Lafayette formation was first named in Mississippi by Iiilgard in 

 1885. This name was suggested by Lafayette county in which the de- 

 posits were found well developed. Later, in 1888, Lewis applied the 

 term Bryn Mawr gravels to a portion of the same formation developed in 

 the hills overlooking Philadelphia, and, in 1891, McGee gave the name 

 Appomattox to that portion of the same deposit which was developed in 

 the Middle Atlantic slope. It was later considered by McGee that his 

 Appomattox was equivalent to Lafayette, and that name has come to be 

 universally accepted as applicable to the entire formation. 



Areal Distribution. — The Lafayette is one of the most widely de- 

 veloped formations of the Coastal Plain, extending from Pennsylvania to 

 Florida and thence westward along the shores of the Gulf of Mexico 

 (Plate II) . Within Maryland it crosses the State from northeast to south- 

 west and is confined to the eastern margin of the Piedmont Plateau and 

 the western border of the Coastal Plain (Plate I). Throughout this 

 area it is believed to have once extended as a continuous bed and it doubt- 

 less, when first deposited, spread westward over a considerable surface of 

 the Piedmont Plateau and eastward over the Coastal Plain; but at the 

 present time it has suffered so from erosion that in Maryland it has been 

 reduced to a mere fragment of its former extent. The largest area is 

 located on the Coastal Plain southeast of Washington where it forms 

 the divide between the Patuxent aud Potomac rivers as far south as 

 Charlotte Hall. This area has been much dissected by stream erosion 

 and around its borders there are many outliers which have been separated 

 from the larger mass by the removal of the material which once connected 



7 When it is remembered that the Lafayette formation was first named in 

 northern Mississippi before the other surficial deposits were recognized, and 

 traced northward along the Atlantic slope to Fredericksburg, Va., by McGee, 

 who was not supplied with adequate maps, then over into Maryland by Darton, 

 who failed to differentiate it from the Sunderland formation, but mapped the 

 two as one, may it not be possible that future investigations will show, when 

 the Maryland horizons are ultimately traced southward, to Mississippi, on 

 large scale topographic maps, that the formation which is now referred to the 

 Lafayette in the northern extension of the Coastal Plain may prove to be 

 very different from the one Hilgard named Lafayette in the Gulf Slope? 



