EFFECT OF CHANGING TEMPERATURES 



27 



effects of changing temperatures are best seen where several of them 

 are associated. 



The importance of this method of rock-breaking is rarely appre- 

 ciated except by those familiar with high and dry regions. Moun- 

 tain climbers know that most high peaks are covered with broken 

 rock to such an extent as to make their ascent dangerous to the 

 uninitiated. High serrate peaks, especially of crystalline rock, are, 

 as a rule, literally crumbling to pieces (Fig. 17). The piles of talus 

 which lie on the slopes and at the bases of steep mountains are in 

 some cases hundreds of feet in height, and their materials are in 



Fig. 18. Serrate mountain peaks with abundant talus. Cascade Mts., Wash. 



large part the result of the process here under discussion. Masses 

 of rock, scores and even hundreds of pounds in weight, are some- 

 times detached in this way, and started downward, and small pieces are 

 much more common. The sharp peaks which mark the summits of 

 most high mountain ranges (Fig. 18) are largely developed by the 

 process here outlined. Even in low latitudes and moist climates 

 the effects of temperature changes may be seen. For example, 

 thin beds of limestone at the bottoms of quarries have been known 

 to expand under the heat of the sun, so as to arch up and break. 



