North Atlantic Pleistocene Problem — Shattnck. 89 
ioned ; but they are not fluvial. * * * The forces con- 
cerned in the formation of the Middle Atlantic slope terraces 
acted horizontally over great distances and with uniform en- 
erg}^ for a considerable period, filling depressions, softening 
contours, and obliterating relief, yet so' gently that essential 
homogeneity of deposit in the horizontal direction and essen- 
tial uniformity in surface prevails for miles. Only the undu- 
latory and horizontally acting force of waves appears compe- 
tent to produce sO' great expanses of uniform surface and con- 
stant structure as are exhibited in this region." 
A summary of Mr. McGee's views regarding the various 
land movements as expressed by the present state of the La- 
favette and Columbia deposits is as follows : 
Post-Chesapeake, elevation and erosion. 
Lafayette (Pliocene?), depression and deposition. 
Post-Lafayette, elevation and erosion of at least 500 
feet ; present topography defined. 
Early Columbia (Pleistocene), depression of about 200 feet and de- 
position. 
Post-Early Columbia, elevation and erosion. 
Later Columbia, depression of about 100 feet and de- 
position. 
Post-Later Columbia, elevation and erosion. 
Present, depression and deposition. 
At the New York meeting^'of the American Association for 
the Advancement of Science during the summer of 1900, jMr. 
McGee took occasion to refer to certain relations of the gravels 
as developed in the vicinity of Washington. After reviewing 
briefly the various deposits which occur in that region, he is 
reported by Mr. J. A. Holmes as making the following state- 
ment.* 
"In a few" localities, especially in the deep cutting in the 
200-foot terrace at the end of Sixteenth street, deposits have 
been observed which fail to fit into this series. This cutting 
reveals, unconformably beneath the Earlier Columbia and un- 
conformably above the Potomac, a heavy deposit of loam and 
gravel of a structure, composition, texture and material sim- 
ulating the Earlier Columbia formation in its normal aspect, 
save that the materials are more extensively disintegrated and 
decomposed. The resemblance of the deposit to the Earlier 
Columbia is such that it might readily be classed with that 
*Science, a. s., Vol. xii, 1900, pp. 990-991. 
