Davis.] 
324 
[Nov. 18, 
2. This over-long introduction has been written out in order 
to place before the reader a general history of the valley that 
contains the deposits made by the Catskill stream when its post- 
Tertiary trench was estuaried ; in order that the special study of 
the deposits here recorded may be viewed in their relations to the 
earlier stages of the history of the great valley. 
The post-glacial submergence, during which the clays were 
deposited, has been referred to as of sufficient amount to allow 
beds, that are now raised 150 or more feet above tide-level, to 
have been laid down as bottom deposits in relatively still water. 
The even upper surface of the clays cannot itself give close indi- 
cation of the amount of depression during their deposition ; this 
must be measured by means of the position of correlated littoral 
deposits, such as the deltas of inflowing streams. 
There is little mention of these deltas in our geological litera- 
ture. In the Geology of the First District of New York (1843), 
Mather said : — “The larger sand and gravel deposits, as the supe- 
rior members of the quaternary [the Champlain clays of the 
Hudson], have been deposited at the confluence of great valleys” 
(p. 148) . He mentioned the great plains of sand about Saratoga, 
where the Hudson river enters the great Lake Champlain-Hudson 
valley from the west ; the vast plain with dunes between Schenec- 
tady and Albany, where the Mohawk enters ; and others of less 
size ; but he did not regard them as deltas. 
The recent account of these deposits by F. J. H. Merrill 1 
gives more definite information as to the amount of post-glacial 
submergence. It is indeed in good part from the incentive of 
this article that I made the observations on the Catskill here 
recorded, during the visit of the Harvard Summer School of 
Geology at Catskill, last July. Mr. Merrill states that “the post- 
glacial deposits of the Hudson River valley .... are of two gen- 
eral types : estuary formations of stratified clay and fine sand depos- 
ited in still water, and cross bedded delta deposits of coarser 
material. . . . Their materials were apparently brought into the 
estuary by tributary streams which dropped the coarser particles 
near their mouths, while the finer rock flour was carried on in a 
state of suspension, and was finally precipitated to form beds of 
1 On the Post-Glacial history of the'Hudson River valley. Amer. Journ. Science, 
Xli, 1891, 460-466. 
