378 IOWA ACADEMY OF SCIENCE Vol. XXVI, 1919 



This contains a sufficiently high percentage of magnesium car- 

 bonate to class the rock as a fairly typical dolomite. 



4. The white crystals encrusting the foregoing specimen : 



Per Cent 



SiOo ■ 0.18 



Fe.>03 and AI0O3 1.21 



CaCOa ". 81.62 



MgCOa 17.15 



Total 100.16 



This varies quite widely from a true dolomite, as the calcium 

 has quite largely replaced the magnesium. The amount of silica 

 is unusually small which might possibly be expected from the 

 crystalline structure of the material. 



5. A specimen from Bertram, Iowa. The formation lies be- 

 tween Mount Vernon and Cedar Rapids. The rock is gray in 

 color, with numerous light-colored crystals disseminated through 

 the massive rock. Some analytical data had been found which 

 seemed to indicate that the magnesian content of the rock was in 

 excess of the calcium. Our analysis was made with a view to 

 determine whether this were really the case. Two concordant 

 results obtained are as follows : 



Per Cent 



SiOg 0.90 



FeoOg and AI0O3 0.90 



CaCOg " 55.61 



MgCOa 42.58 



Total 99.99 



The figures indicate a rather typical dolomite, as one would 

 naturally expect from similar formations in the neighborhood. 



Cornell College, 

 Mount Vernon. 



