454 KEMP AND BILLINGSLEY SWEET GRASS IIILI.S, MONTANA 



West Butte has the largest amoiuit of the rocks which approach the 

 diabases and basalts. Some of our slides from the summit, of its main 



Figure 5. — Geological Map of East Butte 



laccolith, as earlier remarked, are approximations to typical diabases. 

 While there are exposures which might be correctl}^ classed with trachyte 

 porphyries or syenite porphyries, there are, so far as our. studies have 



