292 Becker — Volcanic Cones and Elastic Limit of Lava. 



The height of a uniform column of this material which will 

 strain its lower surface to the elastic limit is 



= 1280 feet = 390 meters. 



If its specific gravity is 3, the load it will bear at the limit of 

 elasticity per square centimeter is 117 kilos. This is a very 

 reasonable result, for I find in a table compiled from a number 

 of trustworthy sources the following values for the pressure at 

 the breaking point (which is of course greater than that at the 

 elastic limit). Good brick, 100 kilos, pr. sq. cm. ; sandstone, 

 200 ; limestone, 300 ; granite, 600. It is probable that the 

 mean specific gravity of the cone is below 3 and its carrying 

 power not much above that of good brick. A good suite of 

 specimens would be necessary to give this determination much 

 value because of the uncertainty as to the density of the 

 material, but it at least exhibits the method.* 



Figure 2. — Theoretical curve and surveyed section of Sugar Loaf, Siskiyou 

 County, California. The comparison is to be made by vertical transposition. 



2/c 



Elevation of base, 4000 feet; of summit, 6399 feet, c = — . 



P 



Lunar volcanoes. — If p is given the form mg, where m is the 



mass of the unit volume and g the acceleration of gravitation, 



2 k 

 c or — is inversely proportional to g. Hence, if the attraction 



of gravitation at the earth's surface were to diminish c would 



* Since this paper was completed I have had access to the maps of Mt. Shasta, 

 recently made by the U. S. Geological Survey. For the sake of testing the 

 theory set forth above four vertical sections through the summit were prepared 

 by the topographical assistants on lines running north aud south, east and west, 

 northwest and southeast, northeast and southwest. All of these profiles showed 

 a very satisfactory general agreement with the theoretical form and yield a value 

 for k/p of about 1320 feet or within 40 feet of that found for Sugar Loaf, so that 

 considering the roughness of the method the two results are to be regarded as 

 substantially identical. The main mass of Shasta appears to consist of andesites, 

 somewhat "trachytic" in texture. 



