834 
[Assembly 
not form a continuous deposit from the head of the lake to its outlet,, 
but interruptions occur along the margin, wherever the primary strata 
reach the lake shore, so that it properly occurs in small insulated basins, 
whose extent from the shore rarely if ever exceeds four miles. On the 
Vermont side the tertiary covers a much greater extent of surface, and 
reaches from the lake to the base of the Green Mountains, or from 6 
to 12 miles. The heighth above the level of the lake to which the ter- 
tiary extends is about 200 feet. This fact I considered an important 
one to settle, with some degree of accuracy, as it would enable me to 
to estimate approximately the actual extent of the ancient sea from 
which this deposit was formed, and by it also be able to identify with 
the tertiary of Champlain, an analogous formation on the Hudson river, 
which has been considered as belonging to a much older, and also to an 
independent basin. I refer particularly to the Albany clay and sands, 
concerning which there are many questions difficult to solve, on account 
of the absence of organic remains. That I may enable the reader to 
judge for himself on these points, I shall briefly state a few of the most 
important facts bearing upon this question. 
1. The summit level of the Champlain canal, between Troy and 
White Hall, is 147 feet. 
2. I have stated above, that the heighth above the lake, to which the 
tertiary extends, is at least 200 feet. Other evidences exist of the for- 
mer extent of the sea, as the water w^orn surfaces are still distinct on the 
primary rocks. Under the present conditions of the water levels then, 
this ancient sea would not only occupy the Champlain basin, but the 
Hudson also, so that there would be a long continuous arm of the sea 
extending from the Gulf of St. Lawrence to the mouth of the Hudson, 
at New- York. 
3. If we may rely at all on mineralogical characters, the tertiary 
clays and sands of Champlain may be traced far south of the lake to- 
wards the tide waters of the Hudson. The marine exuvia have as yet 
been found only on the borders of the lake, still it is not at all difficult 
to identify it by other characters. 
The above remarks are made on the supposition that the land levels 
at the time of the deposit of the tertiary were the same as now, a 
condition which could not exist without an adilitional supposition very 
difficult, if not impossible to support, viz. that the level of the ocean 
has' changed since this deposit was formed. 
