Pleistocene Geology of Moravia Quadrangle 
351 
DRIFT IN VALLEYS. 
The Stationary position of ice tongues or lobes in valleys is 
generally marked by a loop of drift. The development which 
such loops across valleys may attain is dependent upon the follow- 
ing factors: 
(1) The Load Carried hy the Ice. It is needless to say that ice 
which contains no debris fails to register the position of its front. 
It is equally apparent, however, that in a topography of even 
slight relief the ice while passing over it accumulates some material 
so that where dissection has produced valleys maintaining tongues 
a halt of even short duration will be marked by drift; and that 
greater surface inequality, and a slope of the valley floor toward 
the ice, thus offering obstruction to its progress, furnish the con- 
ditions requisite for the deposition of thicker loops of drift. 
(2) The Grade of the Valley. The velocity of ice-front streams, 
and consequently the load that they are capable of transporting, 
depends on the slope of the valley floor. When these streams have 
slight velocity the debris gathering from the ice is more apt to be 
transported and deposited as a valley train. A sluggish stream, 
or a slackwater condition in front of the ice, offers a favorable 
condition to the building up of a valley train. Probably the topo- 
graphic association, on the supposition that the ice contains a 
good load of rubbish, most conducive to the development of a 
valley-loop, requires also a gentle slope, and a corresponding low 
velocity in the streams leading away from the ice. A valley 
tongue which extends into a static body of water, as was very often 
the case in the Finger lake region, should be marked by con- 
spicuous frontal accumulations of drift. In this case wave work, 
and the tendency of the finer debris to be carried off in suspension, 
are factors that in no wise antagonize the formation of heavy loops. 
(3) The Time Factor. The degree of development of this form 
of drift is directly controlled by the length of time that the ice 
maintains a permanent position : in other words, the period dur- 
ing which the melting and feeding factors are about equal. Even 
this condition requires a little closer analysis since it is evident 
that a low rate of ice-feeding accompanied by equally slight melt- 
ing, thus insuring a permanent position, destroys a minimum of 
ice; a thickened loop of drift in most cases represents the decay 
of much ice. Therefore, when the ratio of feeding and melting. 
