1872.] fol: (pecer: 
§2. The Marine Terraces. 
There are along the seaboard in this region, and in some more in- 
land localities, certain stratified marine deposits, which are very dis- 
tinct from the unmodified subjacent drift. In the basins of Lake 
Champlain and of the River Saint Lawrence, these beds are pecu- 
larly well exhibited. They consist (1) of a fine blue clay, and (2) 
of overlying deposits of brown clays and sands,—the sands and clays 
seeming to be interstratified, and together to constitute a sinele dis- 
tinct formation. These deposits constitute the marine terraces of the 
Newer Plistocene period, named Laurentian by Desor, and so called 
by many who followed up his investigations, though they are now fre- 
quently designated as Champlain. From the occasional presence in 
them of a little bivalve, the lower beds are often termed the Leda 
elay formation; for a like reason, the superior deposits are well 
known as the Saxicava sands and clays. In the underlying blue 
clay, which contains few organic remains, I have found in Maine, 
Western Vermont, and in Canada, Leda porilandica and Astarte 
laurentina. ‘The evidences of life in the Saxicava beds are far more 
abundant. Mollusks, fish, and mammals are represented. In the 
basins of Lake Champlain and of the St. Lawrence, some twenty 
species of marine shells have been found; also the remains of seal, 
and of one or two species of whale. 
As has been already intimated, the mountain of ice that spread 
over the country, from six to ten or twelve thousand feet in thick- 
ness, may have occasioned a slight depression of the land. Again, 
as heretofore hinted, the forniation of such a mountain plateau of 
ice must have drawn heavily upon the ocean, and reduced it to a 
very low level. Meanwhile the attraction of this vast and elevated 
continent of massive ice would tend to draw the remaining waters 
of the sea in this direction; still its level, relatively to that of the 
land, was probably, before the ice began to melt, somewhat lower 
than it is to-day. But afterward, as the thawing went forward, the 
ocean must gradually rise, and, the continent for a while keeping its 
old level, cover some paris of the sea-margin which are now dry 
land, also extend up the low level valleys, and fil them with salt or 
brackish waters. Of course, under such circumstances, a deposit 
would be laid down on the portions covered by the sea. This might 
rest occasionally on solid rock, where this chanced to be bare; oc- 
easionally on typical drift, and in some places on the fresh-water ter- 
races already considered. Such, if I mistake not, is substantially 
