776 W. J. MEAD 



average basalt. The very low soda content of the sediments due 

 to the segregation of that constituent in the sea causes the soda 

 line to fall too far outside the triangle to be shown. If the sedi- 

 ments were derived from the average granite, the lines of the several 

 oxides would come very close to intersecting at a point, but since 

 this is not true, the lines for granite are widely distributed and their 

 intersections fall over a wide area. This is likewise true of the 

 basalt lines. 



The point of intersection of the dotted silica and alumina lines 

 indicates the ratio of shale, sandstone, and limestone containing 

 the same amount of silica and alumina as the average granite. 

 Similarly the intersection of the broken silica and alumina lines 

 indicates the ratio of shale, sandstone, and limestone containing 

 the same amount of silica and alumina as the average basalt. 

 The line connecting these two points of intersection is the locus of the 

 intersections of the silica and alumina lines for any combination of 

 granite and basalt. In this manner lines connecting similar inter- 

 sections of granite und basalt lines have been drawn. // the sedi- 

 ments were derived from some combination of granite and basalt, these 

 lines connecting intersections should intersect at a common point. 

 However, because of the nature of the data, we may expect at best 

 that these lines will intersect within a small area. An examination 

 of the diagram, Fig. i, shows that this is exactly what happens; 

 i.e., there is a distinct tendency for these lines to converge and 

 intersect within a limited area. If the lines connecting intersec- 

 tions crossed each other at a common point, the ratio of granite to 

 basalt would be measured by the ratio of the distances from the 

 point of intersection to the "granite" and "basalt" ends of the 

 lines respectively. 



In order to determine whether there is any tendency toward 

 the expression of a definite ratio of granite to basalt by the grouping 

 of the points of intersection on each of the several connecting lines, 

 these lines have been transferred from Fig. i to Fig. 2, where by 

 means of a proportional triangle each line is automatically divided 

 into ten equal parts. The points of intersection of any line with 

 the other lines are marked by short lines crossing the fine con- 

 sidered. Inspection of the proportional triangle on which these 



