78o 



W. J. MEAD 



by showing more shale, less sandstone, and less limestone, but in a 

 general way is similar in showing the great predominance of shale 

 over the other two sediments. 



Sandsto 



100% 

 Limestone 



Fig. $. — -The lines on the triangle show for each constituent the proportions in 

 which the three sediments combine to yield the same amount of that constituent as 

 the combination of 65 parts granite and 35 parts basalt. Compare mth Fig. 4. 



A further comparison of the combined granite and basalt with 

 Clarke's average igneous rock is afforded by comparing Fig. 4 

 (which represents for Clarke's average exactly what Fig. 3 represents 



