160 NEW YORK STATE MUSEUM 
the overloaded region and this resulted in central depression with 
compensating peripheral elevation. (The latter, being distri- 
buted, was very moderate as compared with the former and may 
be disregarded.) These complementary movements served to 
reduce the grade all round, and in so far as the glacier was 
dependant upon grade for its pressure head, they tended to stag- 
nate such portions of the peripheral ice as were situated where 
conditions were favorable for stagnation. As has been pointed 
out, the area south of the St Lawrence river from the Adirondacks 
eastward was so situated ; and it appears probable, not only that 
the ice south of the mountains lost all motion as a consequence of 
the crustal movement, but also that that movement was suffi- 
ciently rapid to destroy the glacier over the St Lawrence valley 
by floating it in the sea, before the ice to the south had been melted 
Oltes 
So much for theoretic considerations. 
The several stages of retreat of the lobes west of New York 
State, as for example the Erie Lobe already referred to, are 
marked by looped recessional moraines fronted by consistent glacial 
drainage features, sufficiently proving the withdrawal of live ice. 
When such a region is compared with eastern New York and 
New England the contrast is seen to be great. Here is no such 
readable topography: the direct evidence of long, almost con- 
tinuous, morainal ridges is absent. i{n addition, the drainage 
lines south of any assumed position of a retreating ice front, are 
found to be interrupted by the clear record of thick masses of 
stagnant ice. This is the case with what is probably the most 
important transverse belt of drift in the whole area, which has 
been identified and mapped as a recessional moraine, the Ogdens- 
burg-Culver’s Gap moraine of New Jersey. 
unit, it may be called a zone. Within this zone, slight alterations of pres- 
sure or temperature may result in a comparatively sudden fusion of the 
solids which become, in consequence, capable of motion until relief of 
pressure or a lowering of the temperature carries the balance back through 
the critical relation where solidification takes place and rigidity is restored. 
4a The basin of the Salmon river (Loon Lake, Chateaugay and Malone 
quadrangles) should furnish reliable data on this point. From 1800 feet 
down to 500 feet the plains and deltas built into the rotting ice edge afford 
material for tracing the successive steps in the lowering of the ice surface. 
If, as Professor Fairchild has supposed, (N. Y. State Mus. Bul. 209-210) 
the delta at 500 feet just north of Malone was built at sea level the glacier 
was already afloat. If on the other hand the sea did not rise to this level, 
the ice against which this plain was built must have had at least its lower 
part submerged, unless the maximum depression letting in the Hlochelagan 
sea was not synchronous with the presence of the ice, but later. 
