3l6 G. K. GILBERT — CRESCENTIC GOUGES ON GLACIATED SURFACES 



Plate 38. — Disruptive Scars on Granite 



Figure 1. — Overlapping and irregular crescentic gouges. 



The arrow, one foot long, indicates the direction of ice motion. 

 The rock face curves down toward the foreground. Evolu- 

 tion creek, near base of mount Huxley, Sierra Nevada. 



Figure 2.— Annular scar. 



The crack occasioning this scar extends obliquely down in all 

 directions. The rock face is nearly horizontal. The arrow, 

 one foot long, shows the direction of ice motion. Valley of 

 Evolution creek, above Evolution lake, Sierra Nevada. 



Plate 39. — Crescentic Gouges in Tuolumne Canyon 



The part of the canyon represented is nearly opposite Wildcat 

 point, Sierra Nevada, and is approximately in latitude 37° 55', 

 longitude 119° 27'. The canyon floor is here a gigantic stair- 

 way ; the view shows the tread of one of the stairs. The direc- 

 tion of motion is shown by the arrow. The glacier reached this 

 spot by descending a slope of about 25 degrees, and here began 

 to ascend a slope of 2 to 5 degrees. Another steep descent 

 begins at the extreme left. The gouges are so numerous that 

 their overlapping obscures their arrangement in sets. Some 

 of the cracks of the granite are probably remnants of conoid 

 cracks, the gouges with which they were once associated hav- 

 ing been removed by subsequent abrasion. 



