J. D, Dana on a Mohawk-valley Glacier. 245 
aheight of 631 feet above the sea-level, separates this depres- 
sion from that of the lake; but the ridge is regarded as only a 
former beach of the lake.’ 
The ridges of Schoharie county form the western boundary 
of the great Hudson valley depression in that latitude—the east- 
ern making the boundary, if we reckon only to a height of 1000 
to 1500 feet, but the western, through the larger part of Schoharie 
county, if to a height of 2000 feet. 
The preceding facts are mentioned, partly in elucidation of the 
following observations on glacier-markings along the Mohawk 
valley, and partly to show what course investigation must take 
i order to complete our knowledge of the great glaciers of the 
Tegion in the Drift epoch. 
The subject of river-terraces, or stratified Post-tertiary deposits, 
on the Mohawk and its tributaries, is also one of great interest 
In this connection, and merits a thorough examination. The 
deposits have some relation to the Drift, as they belong to the 
epoch immediately following—the Champlain epoch,—and con- 
sist in part, at least, of material that had been transported by 
the ice. They are of unusual extent on the East and West Can- 
ada creeks and other northern tributaries of the Mohawk. 
The town of Cherry Valley is situated on the northern border 
of the southern of the New York plateaus. It is hence near 
the southern margin of the Mohawk valley, being about fifteen 
Ss In a straight line from the river; at the same time, it is 
on one of the tributaries of the Susquehannah river, the general 
Course of whose affluents is southward. O rvations on the 
se scratches of this region have, therefore, a peculiar interest. 
following are the results of important investigations on 
Subject, made by the Rev. William B. Dwight, as recently com- 
municated to the writer. He states in his letter (dated Engle- 
Wood, N. J.,) as follows. 
far as I have observed the glacial scratches of the State 
of New York, they do not conform in their course so much to 
the particular courses of the valleys in which they may be found, 
48 they do to the trend of the general — of valleys. 
“At Cherry Valley, there are two distinct sets of scratches 
Rearly at right angles to each other, and none between these two. 
Both’ of these sets appear tn the valley itself. Neither, however, 
* The depression occupi is situated, like those of nearly all the 
likes of North America, cat t also of the St Tatennadeli-tin les bound- 
“y een the Azoic and Palsozoic areas of the continent; that is, between the 
tea that was comparatively stable dry land from the commencement of the Silurian 
hi °nward, and which reaches from Canada northwest to the Arctic and northeast 
r, and the area, stretching southward, southeastward and southwestward, 
waa, tte Azo, that was during the same time an area of progress and of unstable 
AM. Jour. Sct.—SEconp Series, VoL. XXXV, No. 104.—Maxcu, 1863. 
32 
