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Crescentic cracks which are vertical and, like chatter-marks, are concave 

 forward, may be explained as the result of the difference in stress parallel 

 to the rock-face, arising from differential friction. 



Crescentic gouges are convex forward (downstream). Those here 

 described measure from a few inches to over six feet across. The gouges 

 generally occur in sets, the members of a set being usually of nearly equal 

 size. They occur on both bottoms and walls of glacial troughs. Crescen- 

 tic gouges consist of two elements : a gently sloping, incomplete, conoid frac- 

 ture, on the upstream side; and a subsequent, vertical, crescentic fracture, 

 that forms the downstream side of the gouge. The "conoid" fracture 

 is due to shear from an inclined pressure arising from the downward and 

 forward pressures of the ice, as modified by differential friction. This 

 inclined pressure is thought to have been applied by bowlders acting through 

 a thin cushion of debris or of debris-loaded ice, at places where the ice 

 rose over obstructions. The thin wedge formed by this fracture was 

 broken across vertically, and the crescentic wall produced. This second 

 break is due to stress from the upturning of the edge of the wedge when 

 the formation of the first crack relieved it of compression, and the resistance 

 of the ice pressure against this upturning. 



The author regards the gouges as the result of "a mechanical rhythm 

 of some sort," and suggests that the constant pressure of the ice may induce 

 a group of mechanical rhythms to accumulate stress and strain within the 

 rock, until the breaking-point is reached and a conoid fracture produced, 



c. w. w. 



Geological Reconnaissance 0} the Coast of the Olympic Peninsula, 

 Washington. By Ralph Arnold. (Bulletin of the Geological 

 Society of America, Vol. XVII, pp. 451-68; Pis. 55-58.) 



This paper gives the preliminary results of the first measurement 

 and study of any comprehensive Tertiary section in the Pacific North- 

 west. 



The topography of the Peninsula is not very well known. Its dominant 

 feature is the Olympic Mountains, a rugged alpine group rising to a 

 maximum elevation of 8,200 feet, and having a local relief of about 7,000 

 feet. There are no railroads, wagon roads, or trails in the higher mountains, 

 and considerable areas are almost impassable even to a man afoot. 



Surrounding the higher mountains, especially on the northwest, west, 

 and south sides is a maturely dissected plain, sloping seaward from eleva- 

 tions of 4,500 to 5,000 feet. The streams crossing this plain, in fact all 

 the streams of the Peninsula, flow nearly straight outward from the central 



