* 
1894,] Geology and Paleontology. 509 
_ “5th. As suggested to me by Mr. Upham, ‘ The frontal slope of the 
ice surface was then less steep than when the warmer climate, bringing 
the end of the Glacial period, had begun to melt away the southern 
border” At the maximum of extent, the slope may be represented as 
terminating in a very gentle declivity, allowing some transportation of 
bowlders to the boundary, but not generally so steep as to produce 
there any well defined moraine. In the glacial recession the warm 
sunshine and rains were especially efficient, on a belt a few miles or a 
few tens of miles wide adjoining the boundary, so that when any tem- 
porary colder series of years caused a halt or slight re-advance, a 
moraine would be formed.” 
“6th. From the time the ice first entered the headwaters of the 
Allegheny, the Susquehanna, and the Delaware Rivers, the silting up 
of their channels began. This was effected largely by means of the 
excessive amount of the Glacial debris brought within reach of the 
streams. But during the earlier retreat of the ice front from its max- 
imum extent, the silting was facilitated by the differential northerly 
depression, which existed. During a part of this time, also, it was 
facilitated in the Ohio Valley by the Glacial dam at Cincinnati.” 
“Tth. After some thousands of feet of ice had melted off, 
relieving the land from a large part of its burden, the re-elevation of 
the continent began ; (and, as probably the most of the sedimentation 
of the pre-glacial river gorges had been effected during the earlier 
portion of this period of recession), there was then an indefinitely pro- 
longed period of reéxcavation by continuous torrents of comparatively 
clear water, facilitated in the Ohio Valley by the wearing away of the 
Cincinnati dam, which increased by so much the gradient of the 
ream.” 
“8th. When equilibrium had been established again, the land re 
at about its present altitude, but was still covered to a considerable 
depth with ice north of the most prominent moraines. The great size 
of these moraines is partly due to the vast amount of englacial mate- 
rial held in the lower strata of the ice.” 
“9th. The deposits of the so-called Champlain epoch near the 
margin of the glaciated area were considerably earlier in time than 
those which settled over the Champlain Valley itself, since no deposits 
could take place there until the ice had retreated from the area ; but 
these deposits are properly classed together as Champlain, since they 
belong to one epoch of general movement.” ih ih 
“10th. So great a complication of causes was connected with e 
production of all the phenomena connected with the period, that there 
