Studies in the Sierra 



239 



is due to the action of ice and the variously developed cleavage 

 planes and concentric seams which its rocks contain. The 

 architect may build his structures out of any kind of stone, 

 without their forms betraying the physical characters of the 

 stone employed ; but in Sierra architecture, the style alzvays 

 proclaims the nature of the rock. 



In walking the sublime canon streets of the Sierra, when we 

 see an arch spanning the pine groves, we know that there is the 

 section of a glacier-broken dome ; where a gable presents itself, 

 we recognize the split end of a ridge, with diagonal cleavage 

 planes developed atop, and these again cut by a vertical plane in 

 front. Does a sheer precipice spring from the level turf thous- 

 ands of feet into the sky, there we know the rock is very hard, 

 and has but one of its vertical cutting planes developed. If domes 

 and cones appear, there we know the concentric structure pre- 

 dominates. No matter how abundant the glacial force, a verti- 

 cal precipice can not he produced unless its cleavage be vertical, 

 nor a dome without dome structure in the rock acted upon. 

 Therefore, when we say that the glacial ice-sheet and separate 

 glaciers molded the mountains, we must remember that their 

 molding power upon hard granite possessing a strong physical 

 structure is comparatively slight. In such hard, strongly built 

 granite regions, glaciers do not so much mold and shape, as 

 disinter forms already conceived and ripe. The harder the 

 rock, and the better its specialized cleavage planes are devel- 

 oped, the greater will be the degree of controlling power pos- 

 sessed by it over its own forms, as compared with that of the 

 disinterring glacier ; and the softer the rock and more generally 

 developed its cleavage planes, the less able will it be to resist 

 ice action and maintain its own forms. In general, the grain 

 of a rock determines its surface forms; yet it would matter but 

 little what the grain might be — straight, curved, or knotty — if 

 the excavating and sculpturing tool were sharp, because in that 

 case it would cut without reference to the grain. Every car- 

 penter knows that only a dull tool will follow the grain of wood. 

 Such a tool is the glacier, gliding with tremendous pressure 

 past splitting precipices and smooth swelling domes, flexible 

 as the wind, yet hard-tempered as steel. Mighty as its effects 

 appear to us, it has only developed the predestined forms of 

 mountain beauty which were ready and waiting to receive the 

 baptism of light. 



