246 



William E. Ford, 



different sections of the field. This irregularity of the specific 

 gravities was pointed out above. In the case of the calcite por- 

 tion of the field these lines are practically vertical and cross those 



CaCOj 



CaCO, 



Fig. 



of the refractive indices at fairly blunt angles. Fig. 7 shows the 

 portion of the projection occupied by dolomite with the lines of 

 equal refractive indices and specific gravities shown by the solid 



CaCO- 



^reCO, 



FeCOs 

 d- 3.69 



Fig. 9. 



