57 2 THE JOURNAL OF GEOLOGY. 



Harris, 1 is equivalent to a small member near the lower portion 

 of the Eocene series of the Gulf region. 



The Chesapeake formation consists of clays and fine sands 

 with large amounts of diatom remains in the lower members. Its 

 thickness is about 800 feet in eastern Maryland and Virginia, 

 but it is only from fifteen to thirty feet thick about Washington, 

 and is thin all along its western edge. In New Jersey, it is over 

 1,400 feet thick in artesian wells at Atlantic City, but here it 

 includes a lower series, the Shiloh marls, which do not reach the 

 surface in Maryland and Virginia. In the Gulf region, there are 

 still older Miocene members. The youngest members so far 

 studied are found in the Yorkton-Suffolk region, in Virginia, and 

 these are at about the horizon of the youngest Miocene known. 



The Lafayette formation consists of bowlders, gravels, and 

 sands westward, but the materials become finer to the eastward 

 and southward. It is a thin sheet varying from fifteen to twenty 

 feet in thickness in greater part. It overlaps the edges of pre- 

 ceding formations, and its western edge extends for some dis- 

 tance on the crystalline rocks in the Piedmont plateau. A shore 

 formation of talus and bowlders along the eastern foot of the 

 Catoctin Range is of this age, and according to Mr. Keith there 

 are outliers on a high summit a short distance eastward. 



As before mentioned these formations are the products of 

 the base-levelling of the Piedmont region. They are separated 

 by erosion intervals, during which base-levelling extended over 

 the Coastal plain region. 



The western thinning of the Pamunkey and Chesapeake for- 

 mations may be due entirely to increased uplift and planing in 

 that direction, but there is some meagre stratigraphic evidence 

 that the original deposits thickened eastward, and that there are 

 older members in that direction which are overlapped westward 

 by the later deposits of the formations. Throughout its course, 

 the Pamunkey formation is overlapped westward by the Chesa- 

 peake formation, although at a few localities, the overlying 

 Chesapeake beds have been removed locally. The original 



'Am, Jour. Sci., 3d Ser., Vol. XLVIL, April, 1894, pp. 301-304. 



