422 blackwelder: new formations in Wyoming 



18. Dolomite; dense chocolate brown 1| 



17. Shale; pale green sandy shale, with laminae of white sand- 

 stone and buff dolomite 14| 



16. Sandstone; strong cross-bedded white sandstone ^ 



15. Dolomite and shale; pale drab to brownish dolomite, and 



calcareous shale 18 



14. Dolomite ; massive gray to brown 2 



13. Shale and dolomite; gray calcareous shale, and slaty brown 



dolomite 6| 



12. Dolomite; massive, crystalhne, sepia brown, rich in petroleum 



and slightly fossiliferous (Atrypa reticularis, etc.) 11^ 



11. Shale; olive gray calcareous, weathering green 4 



10. Dolomite; thin bedded to massive, drab-brown, and con- 

 taining geodes of jet 16 



9. Shale; sandy to calcareous drab to gray, weathering green, 



with thin layers of gray dolomite 15| 



8. Dolomite; dense gray argillaceous dolomite, with one layer 



of shaly black chert and some geodes like the last 8^ 



7. Shale ; drab calcareous, and associated with dolomite beds .. . 7 



6. Dolomite; slaty, brittle, gray and brown 30 



5. Shale; black to gray, calcareous 2 



4. Dolomite ; dark smoky brown to yellowish, rich in petroleum . . 30 

 3. Dolomite; dense, brittle, finely laminated, white and laven- 

 der 2 



2. Dolomite; olive green, becoming gray above. Probably dis- 



conf ormable at base 22 



428^ 

 Leigh dolomite member of Bighorn dolomite 



1. Dolomite; thin-bedded cream-colored, dense and ringing. 



DORWIN sandstone MEMBER OF THE AMSDEN FORMATION 



. As defined by Darton, the Amsden formation included the 

 sandstones, shales, and dolomites intervening between the 

 Madison limestone below and the Tensleep sandstone above. 

 Throughout western Wyoming the Amsden is divisible into two 

 very distinct parts — an upper division of shales, sandstones, and 

 dolomites of weak character, and a lower, massive, resistant 

 sandstone. On account of their difference in resistance to ero- 

 sion, the upper member has generally been stripped off, while 

 the lower remains capping the mountains and ridges of Madison 

 limestone. It therefore became advisable in practice to map 

 the two members separately. To the lower sandstone the name 



