176 



PHYSIOGRAPHY 



posed largely of cinders, etc., are worn away with comparative ease, 

 while those of lava are more resistant. Among the many extinct 

 volcanic peaks in the western part of the United States, it is possible 

 to find illustrations of cones in various stages of destruction. Only 

 those of recent origin still show their original forms, or forms but 

 slightly modified. None but recent cones retain their craters, or 

 the symmetrical slopes they once possessed. Volcanic cones in the 

 sea or in lakes are attacked by waves, and small cones in the sea 

 are soon worn away. The case of Graham Island is an example. 



Examples of fresh cones. In Arizona, California (Fig. 174), 

 Idaho, Oregon, and elsewhere in the United States there are vol- 



Fig. 174. Typical cinder cone, Clayton Valley, Cal. 



canic cones so recently formed that they have suffered but little 

 erosion. Cones of similar freshness are found in other lands. 



Examples of worn cones. ML Shasta rises two miles above a 

 base seventeen miles in diameter, to a height of 14,350 feet above 

 the sea. It is partly of lava and partly of fragmental material. 

 Its upper slopes are steep and furrowed with ravines. About 2,000 

 feet below the summit on the west side is a fresher and therefore 

 younger cone (Shastina) with a crater in its top. Remains of more 

 than 20 smaller cones also occur on the lower flanks of the main 

 mountain. Mt. Shasta is a good example of a volcano which has 

 suffered some erosion, but there is still abundant evidence of rather 

 recent eruptions. 



