390 The American Geologist. June, i897 
Canary islands for instance, in a depth of 6,000 feet.* Simi- 
lar conditions must liave prevailed in the eastern border re- 
gion ; hence the absence of the typical Utica shale and its 
fauna in eastern New York and the region east of the latter,f 
its fast increase in volume towards west,J from where the 
material could not have come. At Glens Falls the velocity 
was still too great to allow the deposition of the fine detritus; 
but in entering the wide continental sea, the current rapidly 
decreased in velocity and consequently the increase in the 
thickness of the deposits until the maximum of sedimentation 
seems to be reached at the present site of Utica. where also 
the obstruction to the current from the projecting Adirondack 
land is removed and the waters, being allowed to spread a lit- 
tle towards the north (the readings obtained at Deerfield seem 
here to be significant), a somewhat abrupt decrease in the 
velocity of the current must have occurrt^d. This, however, 
must necessarily have resulted in a sudden increase of the 
quantity of sediment. As the current now, on its W. S. W. 
progress left all shores behind, it received no new supply of 
terrigenous sediment, hence, the rapid decrease again to the 
west of Utica, as indicated by the measurements obtained in 
drilling wells in the western part of the state. In a well at 
Chittennago, south of Oneida ]ake,only 200 feet of Utica shale 
have been met with. But then, this decreased Utica shale 
extends over a wide area, as far as the Ohio river, in the di- 
rection of the observed current, while it thins out towards 
the north and northwest, where the Galena limestone formed 
at the same time. In those regions to which the current 
could not carry its silt, the diiference in temperature and sal- 
inity which necessarily must have existed between the cur- 
rent water and the quiet Trenton sen, were sufficient to pro- 
duce a change in the fauna, though the limestone formation 
did not cease. These ditferenees may have been only slight, 
for the fauna of the deeper littoral zones, in which the lime- 
stones probably formed, is known to be very sensitive to such 
d i ife r e n c e s^^ 
*T. M. Reade, Phil. Mag. vol. xxv, p. 392. 
tWalcott states that the fauna of the upper part alone of the Utica 
foruiation occurs within the valley of the Hudson. 
JDana (op. cit. p. 196) gives only 15 to 35 feet at Glens falls, while in 
Montgomery county it is 250 feet and near Utica amounts to 710 feet. 
