678 JUNIUS HENDERSON 



of small glaciers formed and later coalesced, and in its retreat it 

 was doubtless broken up into a number of separate ice masses 

 before final disappearance, which history would be reflected in 

 the number and character of the moraines. 



The glaciated shelf is everywhere covered with a thick sheet 

 of ground moraine. For this reason there is a great scarcity of 

 roches moutonnees and glacial striae. 



On top of the mesa different conditions produced very different 

 results. There was no crest or cliff back of which drifting snow 

 could accumulate for the formation of a glacier which would extend 

 to the southwest, or that would furnish abundant material for 

 the construction of moraines. A large, broad glacier, or perhaps 

 more than one, formed on or near the highest point along the north- 

 east rim and moved in a southwesterly direction along the gentle 

 slope of the mesa. It built a long, low terminal moraine across the 

 mesa near its middle, which now incloses several shallow lakes. 

 Owing to the absence of ground moraine, its course is marked by 

 numerous low, well-rounded roches moutonnees, but recessional mo- 

 raines are absent or scarce and not well defined. The basalt 

 weathers readily, so no traces of glacial striae were observed, but 

 fluting was observed in several places. There are large morainal 

 lakes on top near the eastern end of the mesa, but time did not 

 permit their investigation. We found no clear evidence of gla- 

 ciation on the western half of the mesa top. Because of the to- 

 pography we believe the glacier (or glaciers) on top could not have 

 been formed to any large extent by drifted snow, and that the 

 glacier was probably rather shallow in proportion to its width and 

 length. 



