1872.] 13 5 [Perry. 
parts at least, they are, as already intimated, terraces of fresh-water 
origin. They consist sometimes of clay, sometimes of sand, while 
occasionally there is a blending of the two; their stratification, al- 
though irregular in places, is generally distinct, and they were doubt- 
less laid down by the waters which flowed from the wasting ice-sheet. 
The places they occupy were usually low plains, though in some 
eases they were the basins of ponds and lakes, which must have been 
very abundant during the later Glacial times; while often they were 
simply mud-flats and sand-flats, clay and sand being deposited in 
different parts according to the varying conditions prevalent in the 
neighborhood. Directly below them unmodified drift may be usually 
found; immediately above these fresh-water terrace beds there 
occur in some localities the marine deposits of the terrace period. 
Thus, of course, where clay rests upon clay, or sand upon sand, and 
there are no other indications, it is difficult to discriminate between 
them. But in many cases each set exists by itself, the one in places 
holding marine remains, and the other never, and so situated that 
there need be no reasonable question as to their respective modes of 
origin. This point having been worked out by patient observation in 
favorable localities, it has been my aim, so far as I have had oppor- 
tunity and leisure for the work in new neighborhoods, to seek for the 
means of discrimination between these intermediate beds, which at 
first sight often seem to be identical, or at least of substantially the 
same age. In this direction an important task of discrimination still 
remains to be prosecuted in many parts of New England, upon the 
superficial stratified deposits lying between the level of the ocean 
and five hundred feet above it, and specially upon such as occur along 
the seaboard. 
In the light of what has been advanced, I venture to suggest that 
many stratified deposits which have been regarded as oceanic are 
fresh water beds of the Terrace period, while these are here and 
_ there overlaid by true marine strata characteristic of the later por- 
tion of the same times. Thus, not a few beds which Prof. Dana 
calls Champlain (marine) are no doubt of fresh water origin, and 
were deposited toward the end of the Drift, or in the early part of 
the Terrace period. This is the case in various different sections 
of New Eneland, and perhaps more particularly in the New Haven 
region. In the superficial formations occurring in and about the lat- 
ter place, as Prof. Dana admits, no marine remains have been found. ! 
1 Paper cited, p. 87. 
