44 JOSEPH BARRELL 



limit of capacity for sustaining stress-differences is apparently of the 

 order of i,ooo pounds per square inch, though its weakness may be 

 masked to some extent by the strength above. From the evi- 

 dence, however, it seems capable of carrying stresses of more than 

 loo pounds per square inch, but is clearly incapable of carrying 

 stresses of as much as 5,000 pounds per square inch. To reach a 



TABLE XXX 



Estimated Approximate Ratios Giving the Variation of Strength 

 WITH Depth as Shown by the Nature oe Departures from 



isostasy 



lithosphere 



Depth in Kilometers 



Strength in Percentage 







100 



20 



400 



25 



500 



30 



400 



50 



25 



100 



17 





asthenosphere 



Depth in Kilometers 



Strength in Percentage 



200 



8 



300 



S 



400 



4 



more definite conclusion the subject must be tested from many 

 angles and is a problem for the geophysicist rather than for the 

 geologist, but the results are of geological importance and the 

 geologic and geodetic data may turn out to have more determina- 

 tive value on the distribution of strength than the evidence from 

 tides and earthquakes. 



[To he continued] 



