NORTHERN BOULDERS. 
337 
elevation of some portions above water might produce counter currents; and finally, after the 
land had risen to within eight hundred or one thousand feet of its present elevation, the great 
valley of Lake Ontario would form a broad bay, communicating with the ocean through the 
valleys of the Mohawk and the Susquehannah, while the communication by the valley of the 
Mississippi was becoming closed. Even for a long period after this, the bay of Lake Ontario 
would communicate with the ocean by the valleys of the St. Lawrence and the Mohawk, 
while the valley of the Hudson formed a narrow strait, with numerous inlets and bays; the 
granite mountains of Northern New-York and of the Highlands, and the old red sandstone of 
the Catskills, rising to the height of from two thousand to four thousand feet above its level. 
I have enumerated only those mountainous regions of New-York and New-England with 
which I am familiar. Of the elevated country in Canada, north of Lake Ontario and the St. 
Lawrence, too little is known to speak with certainty ; but it is extremely probable that this 
also has furnished its share of the transported materials, which we now find in the valley of 
Lake Ontario and Western New-York. Farther west, there remains no doubt but the country 
on the north of the great lakes has furnished the boulders of Ohio, Indiana arid Illinois ; and 
as these mountains become more elevated toward the sources of the Mississippi and farther 
to the northwest, they have been the source of a much greater number of boulders over the 
country west of the Mississippi, than farther east. 
We have also to inquire what collateral proof we have of this condition of the continent, 
besides the dispersion of the boulders. I have before alluded to the deposits of newer tertiary 
extending through the valleys of Lake Champlain and the St. Lawrence, which contain marine 
shells of species existing in the present ocean. Similar deposits, but without the shells, exist 
in the valleys of the Hudson and Lake Ontario. These have been subsequent to the great 
abrading and denuding agency which has excavated the valleys and scored the surface of the 
rocky strata, and previously to, or in part formed during the period of the transportation of 
the granitic boulders. 
This Tertiary deposit on Lake Champlain is elevated in some parts nearly three hundred 
feet above the lake, which shows a depression of the present level, at the time of its formation, 
at least four hundred feet. This would be sufficient to raise the water of the ocean about one 
hundred and seventy feet above Lake Ontario, or nearly to the elevation of the ancient ridge 
bounding that lake.* The boulders of Primary rocks are distributed over the surface of this 
fossiliferous deposit, and in some places imbedded in it. In speaking of their occurrence in 
the tertiary of the St. Lawrence valley, Capt. Bayfield says, “ They are found in the cliffs at 
different levels, not resting upon each other, but as if they had been dropped there at widely 
different times, during a long period, in which a quiet deposition of clay, sand and gravel had 
been going on, and in which the different genera of testacea had lived and died. Some of the 
shells are of course broken, and some of the valves are separated, as is the case in the bottom 
of the present sea; but many have both valves together, although they separate when taken 
up, because the ligament no longer exists. All idea of these shells (together with the sand, 
* The level of Lake Champlain is ninety-three feet above tide water. 
43 
[Geol. 4th Dist.] 
