774 



W. J. MEAD 



to recalculate the analyses of the sediments, excluding these con- 

 stituents. The analyses of the igneous rocks are recalculated on 

 a water-free basis. Since the problem does not permit of a rigorous 

 solution, graphic methods have been used which permit of viewing 

 in perspective, as it were, the various relations and conceptions 

 involved. 



TABLE I 



SiO. 



AlA 



FeA 



FeO 



MgO 



CaO 



Na.O..-. .. 



K.0 



TiO' 



P3OS 



Totals 

 Fe 



70.47 



14.90 



1.63 



2. 17 



331 

 4.10 



•39 



.24 



49 65 

 16.13 



5-47 

 6.45 

 6. 14 

 9.07 



3-24 

 1.66 

 1. 41 



99.87 

 2-45 



99.70 



91.29 



100.04 

 5 19 



93.61 



95 

 10 



i5\ 

 32] 



25 



90 

 48 



41 

 27 

 085 



519 



99915 

 055 



57-53 



9.02 

 1. 41 



■94 



13 -74 



74.10 



.09 



•57 

 . 10 

 .07 



100.04 

 .66 



1. Average granite. 



2. Average basalt. 



3. Average shale. 



4. Average shale recalculated to 100 per cent, omitting H3O and CO3. 



5. Average sandstone. 



6. Average sandstone recalculated to 100 per cent, omitting H2O and CO2. 



7. Average limestone. 



8. Average limestone recalculated to 100 per cent, omitting H2O and COa. 



Trilinear co-ordinates are used in Fig. i; the triangle labeled 

 in the corners ''Shale," "Limestone," and "Sandstone," respec- 

 tively, serves as a base on which ratios of these three components 

 may be indicated by points, and a series of ratios represented by 

 lines.. The algebraic sum of the perpendicular distances from any 

 point inside or outside of the triangle to the three sides of the tri- 

 angle or their extensions equals the altitude of the triangle, con- 

 sidering distances toward the opposite apex as positive, and 

 distances away from the opposite apex as negative. Any point 

 on the dotted line labeled "SiOz, Gr.^^ represents in parts per hundred 

 the ratio in which shale, sandstone, and limestone may he combined 

 to yield the same amount of silica as the average granite. This line 

 is obtained by finding the proportion in which sandstone and lime- 



