Pleistocene Geology of Moravia Quadrangle 367 
of the latter condition is dependent directly upon the slope of the 
valley in which the tongue lies; only when the valley slopes away 
from the tongue would this vigorous drainage at the axis of the 
valley obtain. (3) Reports of existing glaciers of a type more 
analogous to the lobes that characterized the front of the ice-cap 
often mention the tendency of crevasses to reach inward from 
the lateral slopes of the valley tongue. When the ice is relatively 
stagnant and the conditions of drainage exist as described under 
No. 2, these crevasses would not only be filled with rubbish, but^ 
with the normal melting would be enlarged till the accumulation 
of debris prevented further melting. Such conditions would 
account for some of the ridges of drift that are so reticulated in 
arrangement as to make their interpretation as valley loops absurd. 
Another feature of the above discussion follows as a corollary 
when there is a large amount of clay present in the drift. The 
scars of recent land-slips in the very areas under discussion show 
how at the present time the irregularity of the drift is being empha- 
sized. Glacial till in which clay predominates weathers more per- 
haps through solifluction than through erosion, and while soli- 
fluction need not necessarily render a topography more irregular, 
it is evident that wet clay when moving in mass produces scar- 
slopes that are much sharper than the initial surface. 
The best illustrations on the quadrangle of drift of this hetero- 
geneous type exist in the Skaneateles Inlet valley (fig. 13) and in 
the valley southeast of Morse Mill. Milder surfaces, though similar 
perhaps in genesis, are noted in the Fall Creek valley north of 
McLean against the west slope, and northeast of Groton in the 
Freeville-Moravia valley. 
(2) Terraces. Along the walls of valleys once occupied by 
tongues of ice are found terraces formed of materials dropped 
from the ice, and of debris deposited by marginal streams. Dur- 
ing the continuance of the glacier, these deposits tended to level 
up the depressions between the ice and the valley wall. Where- 
ever this marginal drainage was locally slack, or was temporarily 
ponded, much clay entered into the debris being collected. At 
the melting back of the glacier, the ice-contact face of these 
deposits assumed a lower angle, as shown by Watson.^ The 
^Tarr: Zettschrift fur Gletscherkunde, band iii (1908), p. 87. 
* New Tork State Museum Report^ vol. 51 (1897), p. 178, figs. 12, 13. 
