Perry.] 122 [February 28, 
(1I.) THE TERRACE PERIOD, 
Which comes next in order, might be called, according to the no- 
menclature of Sir Charles Lyell, the Newer Plistocene period, and 
the deposits made during its continuance, the Upper Plistocene 
formation. The designation adopted, however, is more simple, and 
on the whole, is perhaps freer from objection than any other. It is 
true that terraces belong to different times ; that some, as has been 
already intimated, were formed shortly after the middle of the main 
Ice-period ; while much of the work, which gives the terraces a 
striking peculiarity in their appearance, was done at a later day. 
Still, as the time now to come under consideration was especially 
characterized by the formation of terraces, it may be styled the Ter- 
race period. Meanwhile it should be distinctly borne in mind that 
this and the preceding period mutually overlap ; that the local gla- 
ciers continue into the New England Terrace period, and were prom- 
inent in it; that the terraces extend back into the closing part of the 
Ice-period, and from it derive some of their characteristic features ; 
that still, as formations, the drift proper and the terraces are strik- 
ingly unlike ; and that generally the latter overlie the former. ‘The 
terraces being thus superior to typical drift it may be remarked that 
they are strictly of two kinds, viz., fresh-water and marine ; as such 
they may be conveniently considered separately. 
§1. The Fresh-Water Terraces. 
- 
These generally consist of two parts, (1) of clay and (2) of sand. 
More usually the clay is at the bottom and the sand above; still they 
run into each other, to a considerable extent, as was natural from 
their mode of formation. The clay, especially where it has not been 
exposed to the atmosphere, is of a deep blue color, and in many 
localities very remarkable for its tenacity. Many elements, varying 
according to local circumstances, enter into the composition of the 
sands, which are greatly unlike as to degrees of fineness and coarse- 
ness in different places, and even in the lower and upper portions of 
the same beds. Thus these fresh-water beds have a distinctive char- 
acter, and are readily discriminated from the underlying Drift. If 
we would secure a right understanding of their varying cbaracter- 
istics, we must notice somewhat more in detail their mode of origin. 
The summer of the ages returning in the northern hemisphere, the 
ice-sheet gradually melting and retreating northward, the wasting of 
