Perry.] 94 [February 28, 
isolated masses of ice, moving toward the east or west, is just what 
occurs, only more rapidly, in the case of water. Small streams, 
having a given course, lose themselves in the mighty deluge which 
sweeps over the country at right angles to their trend. Their in- 
dividual identity is no longer maintained; they are swallowed up in 
the vast stream, and themselves flow on an indistinguishable part of 
its madly rushing current. Substantially this, according to the evi- 
dence, only at a slowly-lingering pace, perhaps took place in the 
transition from the Earlier to the Middle Glacial times. ~ The general 
erosion, smoothing, and furrowing of the rocks show that the force 
passed the east-west valleys and hills nearly at right angles to their 
trend. Connected with this change in the direction of the force ex- 
erted, the markings of the opening glacial period must have been, 
for the most part, erased. Indeed, such a change and its long con- 
tinuance would result in the obliteration of all the eariier vestiges of 
ice-action, and to the inscription of new characters, peculiar to the 
middle Ice period. And these later markings must have been writ- 
ten on the surface of the solid frame-work of the whole country, just 
as we find them, north-south in their direction, and suited to tell 
their characteristic story. Thus what were probably local east-west 
glaciers being turned from the course which they originally followed, 
the whole mass would move southward, often modified somewhat in 
its direction, but never entirely deflected, by local barriers. 
Brief reference should be here made to an evident misconception 
on the part of Professor Dana. So far as I can see, his discrimina- 
tion between the main ice-sheet and local glaciers recognizes, not 
difference in time, but simply upper and lower portions of a vast ice- 
blanket,—such inferior parts of the great ice-mass as occupied val- 
leys, and the like, being in his view local glaciers. He seems to sup- 
pose that the superior portion of the main mass was largely distinct 
from the lower; that there was this general glacial sheet which 
spread widely over the country, and had its peculiar motion and 
direction; that there were beneath it, and to a great extent separate 
from it, many local glaciers, each having its characteristic features, 
and moving for the most part independent of the overlying ice- 
stream; and that thus there were, above and below, at one and the 
same time, not merely a difference in position, but also in motion, 
and that the lower part of the mass had a distinct and an essentially 
different direction. Such is substantially the impression I have re- 
ceived from Mr. Dana’s paper. It is easy to see, from this point of 
