258 STANTON 



C. M. 79. Tufaceous conglomerate. From near the base of the Bearpaw 

 formation, just below No. 78, at the mouth of Lost Horse 

 Creek, T. 7 N., R. 11 E., sec. 17. This conglomerate consists 

 of rounded pebbles of augite-andesite, or basalt, all of which 

 are very similar to one another. The rock is probably a water- 

 rolled tuff. 



These were selected from the report because they come from the 

 immediate neighborhood in which plants, invertebrates, and verte- 

 brates were obtained from the higher formations and there is no doubt 

 as to the identity of the different horizons. Farther northwest near 

 Summit and Dorsey and along the west side of the Crazy Mountains 

 andesite tuffs are more common, but the marine Cretaceous forma- 

 tions are there not so certainly identified. Only the following wn'll 

 be cited: 



C. M. 14. Trachyte porphyry from Claggett beds 900 feet below fossils 

 (609) determined as Bearpaw. Sec. 4, T. 7 N., R. 9 E. 



C. M. 15. Andesite tuff. From near the base of the Bearpaw; T. 7 N., 

 R. 9 E., sec. 5. Bearpaw fossils collected above. Specimen 

 consists of many feldspar and augite crystals, with some mag- 

 netite and rock fragments with the texture of an andesite 

 groundmass. The rock undoubtedly is essentially a pyroxene 

 andesite tuff. 



The marine Cretaceous fossils collected above these specimens are: 



Ostrea pellucida M. & H. 

 Avicula liuguiformis E. & S. 

 Avicula nchrascana E. & S. 

 Inoceramus cripsi var. harabini Morton 

 Callista deweyi M. & H. 

 Baculites compresses Say 



Brackish-water shells were reported by Weed^® "as occurring 

 northeast of the Crazy Mountains in a bed of limestone, interbedded 

 with the Livingston sandstones and conglomerates, a few hundred 

 feet above the base of the formation." The locality as recorded on 

 the field label is "Muddy Creek west of Gordon Butte and Cotton- 

 wood Creek" and the species identified are: 



Ostrea subtrigonalis E. & S. 



Corbicula cyl/ieri/ormis M. & H. 



Corhula subtrigonalis M. & H. 



Corbula subtrigonalis var. perundata M. & H. 



** Bull. U. S. Geol. Survey, No. 105, p. 33. 



