104 The American Geologist. August, 1903. 
posits in Pennsylvania and New York of this date became 
more sandy and of greater mass, and were attended with an 
influx of fresh water, which may have been, in some degree 
at least, instrumental in rendering the conditions of life un- 
favorable to the previous marine fauna. 
In any case there is little doubt that, as argued by professor 
Hall and others, the sandstones of the northeast, including the 
Oneonta, represent the shore deposits of the Upper Devonian 
and are not exclusively of Catskill date. Their exceeding bar- 
renness of fossils renders proof of the proposition difficult. A 
few brachiopods and a single lamellibranch — Amnigenia cats- 
killensis — are almost the only molluscan fossils known in the 
original Catskill strata. The latter species has a great vertical 
range. It was probably an estuarine form capable of living in 
both salt and fresh water or, at any rate, of enduring great 
variation of salinity. The fish remains that accompany it may 
be explained, as professor Stevenson suggests, by supposing 
that these rapid travellers ran up into places which the slow 
moving mollusks could not reach. But it is equally probable 
that they, too, were estuarine species and were at home in the 
brackish water. Unless, however, they were vegetarians, which 
is unlikely, their presence in strata otherwise so barren is dif- 
ficult of explanation on the ground of scarcity of food. 
The hypsographic changes during the Catskill period Avere 
for the most part merely continuations of those that had been 
inaugurated in the Chemung, with slight variations. A deep 
depression received the Ohio shale and Chemung deposits, 
3000 feet in thickness. The area of this depression was ap- 
apparently smaller during the Catskill period than it had been 
previously, but more profound, inasmuch as the Catskill sand- 
stone covers a smaller space, but is vastly greater in thickness 
than the earlier Chemung, etc. In some places it reaches five, 
six and, occasionally, seven thousand feet, implying subsidence 
to an equal amount. It is noteworthy that this subsidence extend- 
ed up the Hudson estuary where, in the Catskill mountains, a 
vast thickness of this sandstone is found. But beyond that point 
little or no trace remains of its occurrence within the limits of 
Appalachia. The late Devonian subsidence then culminated in 
the formation of a profound catchpit, where sank the coarse 
sand and pebbles that the eastern and northeastern streams 
