180 The American Geolo(/isf. September, 1897 
The Drift. 
This valley as described and sliown in profile, is filled with 
drift to an average hight of about 100 feet above the lake. 
The upper thirty or tifty feet of this consists of sand and 
gravel distinctly stratified, as nia^' be seen in the excavations 
made for buildings. It is the ''delta sand" of Dr. Newberry. 
This sand and gravel was laid in its present position by the 
waves when the lake stood at a higher level than now, and 
shows such wave action most distinctly. The clay l.ying be- 
neath this and constituting the drift, not only fills the valley, 
but forms the covering for the deep rocky bottom of the lake. 
This is called by Dr. Newberry the Erie blue clay, and is "sup- 
posed to be the fresh water and interior equivalent of the 
Champlain clays, which were deposited in the earlier portion 
of the drift period on the Atlantic coast when it was sunk 500 
feet or more beneath the ocean." It is easily recognized by 
its bluish or dark cast and is mixed throughout with Ia3''ers 
of quicksand and gravel and some striated pebbles, mostly of 
Canadian origin. It is devoid of fossils, but in some places 
the delta sand is separated from the clay by a laj'er of car- 
bonaceous matter. Mr. F. S. Gilbert, in drilling a well near 
the public squai'e, passed through a log about two feet in di- 
ameter at a depth of 125 feet from the top of the well, this 
being far below the band of carbonaceous matter. 
The clay as exposed is distinctly laminated and shows un- 
mistakably the action of water. It was laid down on the bot- 
tom of the lake when lake Erie as such did not exist, but was 
a part of a much larger sheet of water, covering probably not 
less than 200,000 square miles. 
Origin of the Valletj. 
It is believed by man}^ that the continent prior to the Ice 
age stood from 3000 to 5000 feet above its present level. From 
among many examples which show such former uplift, may be 
mentioned the case of the Hudson river valley. The contin- 
uation of this submarine channel has been traced by detailed 
surveys to the edge of the continental slope, a distance of 
about 105 miles southeast of Sandy Hook, and 120 miles from 
New York. Its outermost 25 miles are a submarine fjord 3 
miles wide and from 900 to 2250 feet in vertical depth meas- 
