Prof. T. C. Chamberlin. 
49 
fold so formed would be elongated and appressed by the con- 
tinuation of the process and become a layer. The ice, beneath, 
however, would gradually yield, and the debris layer would set- 
tle down out of the line of maximum thrust and the conditions 
for a new fold would be induced. There were several such ap- 
pressed folds or inthrusts on the slope of the embossment in 
question. In several cases in connection with other glaciers, very 
open folds were formed by the debris layers passing directly out 
into the ice in the lee of the embossment, and then gradually 
curving down and becoming reversed, apparently because the 
ice in the lee moved slower than that above. In some of these 
cases it was clear that the layer was formed by rubbing across 
the embossment or some protruding part of it, and that the fold- 
ing was subsequent. So also there were cases of true faulting 
and overthrust, rocky debris being carried along the fault plane. 
The particular mode of inthrust seems therefore to vary some- 
what, but the general method is essentially the same. It is prac- 
tically a process of overthrust, dependent on inequalities at the 
base of the ice. 
METHOD OF MOVEMENT. The structure of the ice, as 
already described, appears to imply that the layers moved as 
units. The sharp definition between the clean ice and the debris 
layers, which was the common fact, indicates the absence, in the 
main, of that heterogeneous admixture of rock-rubbish and ice 
which might be expected if the ice moved as a liquid. The dis- 
tribution of the dirt through the ice was very different from that 
of dirt through water when it is roiled by motion. 
Several other considerations support the interpretation that the 
ice moved by layers, in part at least. On almost every one of 
the vertical faces certain layers were seen to jut out sharply 
above those beneath. Sometimes there were six, eight or ten 
of these projections one above another on the same face, the 
overset ranging from a few inches to a foot or two. In rare 
cases the over jutting reached ten or fifteen feet. At first sight 
this seemed a clear proof of the overthrust of the upper layer, but 
upon more critical study it was seen that there was usually 
earthy matter in the upper part of the under layer, or at the junc- 
