IOWA ACADEMY OF SCIENCES. 19 



ing and meet in sharply defined edpfes. The more common crystallographic forms 

 are the pentagonal dodecahedron, or pyritohedron, and the cube, with all grada- 

 tions between the two. Though small they are perhaps the most perfect crystals of 

 this mineral found in the state up to the present time. 



PvRiTE.— Upper two from Dubuque; lower four from Ft. Madison. 



From the Kinderhoolc clays of Burlington were obtained a number of bright- 

 faced specimens showing the cube with the corners very slightly truncated by the 

 octohedron. These occur sometimes singly, sometimes in aggregates of consider- 

 able size. 



In the black bituminous shales of the Lower Coal Measures at Des Moines occur 

 some rather remarkable specimens of pyrite. The form is the octohedron modified 



