174 



WILLIAM H. HOBBS 



regarded as uniformly dis- 

 tributed throughout a 

 horizontal plane; since, as 

 already stated, anticline 

 formation is believed to 

 occur at such depths that 

 the altitude of the arch is 

 small by comparison. The 

 discussion of the compe- 

 tence of an anticHne differs 

 from that of an arch of 

 masonry, for the reason 

 that the latter receives no 

 external support in a ver- 

 tical direction except at the 

 abutments. An anticline 

 is, upon the other hand, ^ 

 in part supported by the 

 resistance to compression 

 of the weaker formations 

 which are arched beneath 

 it. It may never alone 

 support the entire load 

 which rests upon it; but 

 since it is stronger than 

 immediately inferior beds, 

 it tends always to Hft from 

 them some portion of the 

 load. This portion varies 

 at different parts of the 

 arch, and for any point is 

 roughly proportional to the 

 cosine of the angle which 

 the tangent at that point 

 makes with the vertical 

 (Fig. 14). By a summa- 

 tion of these values for 





