GROUND MORAINE. 277 



feet, and over most of the State very much less; in the slate regions often 

 only a foot or two and from that down to 0. 



GROUND MORAINE. 



Excavations at the bases of the terminal moraines ought to exhibit well 

 the differences between the englacial and the subglacial till. The moment 

 we assiime that the moraines were of englacial origin we are logically 

 driven to look for a different origin for the lower layers of the till. For 

 the matter of the moraines (englacial matter) shows little glaciation, while 

 that of the lower part of the till is intensely glaciated. It is just what 

 should be expected if it is a moraine profonde. Accumulations of it have 

 a curved, flowing outline, quite unlike the heaps into which the englacial 

 till was often thrown. These are the two fundamental arguments for the 

 existence of a ground moraine. Expanded they are as follows : A moraine 

 profonde consists of ddbris that has been between moving ice and the 

 undei'lying rock. A rock fragment can not be in such a situation without 

 being subjected to great attrition against the rock or against other frag- 

 ments if the ice preserves the known rigidity of ice under ordinary condi- 

 tions It has often been assumed that under extremely great pressure ice 

 becomes much more fluent or plastic than at ordinary pressui'es. If this be 

 so, what bearing has the fact on the nature of the glaciation? 



Whatever theory of the origin of the lower or intensely glaciated till 

 we adopt we must make it consistent with two facts: First, all the known 

 excavations that penetrate to the bottom of the till reveal glaciated rock. 

 Either, then, the whole mass of the lower till was rolled or dragged bodily 

 beneath the ice, or each place overrun by the ice was first an area of erosion 

 and subsequently one of deposition. Second, the depth of the rock scor- 

 ings, their straightness and length, require a vast force to produce them. 

 The immense amount of debris that has been fractured or gi-ound to rock 

 flour or scratched and polished is the ample counterpart of the very great 

 abrasion of the rock. No theories of the superior fluidity of ice under 

 enormous pressures or under any other conditions can be allowed to obscxu'e 

 the fact that at the time the rocks were scored the stones that did the work 

 were moving under great pressures and with wonderful steadiness of move- 

 ment. The increase in plasticity, if such there was, was not sufficient to 

 impair seriously the rigidity of the ice. If the stones that were ground 



