402 Bulletin American Museum of Natural History. [Vol, XVI, 



side of the Hills, a thick bed of sandstone immediately over- 

 lies the Triassic; but this bed is everywhere lacking on 

 the west side of the Hills", the transition being uninterrupted, 

 and seen only in the change from sandy red clay to sandy 

 green clay. 



On comparing the sections made on the east side of the 

 Hills, ^ these on the west side, and similar sections made in 

 central and eastern Wyoming, ^ it becomes clear that the 

 Jurassic of the west side corresponds more closely with that in 

 central Wyoming (especially on the Medicine and Como anti- 

 clines) than the west side corresponds to the Jurassic on the 

 east side of the Black Hills. However, the upper or fresh- 

 water beds of the east and west sides correspond with one 

 another better than the marine layers. Many of the most 

 striking layers of the west side can be detected in the centre 

 of Wyoming almost exactly as they occur in the Hills. To 

 bring this out strongly, in the table where the sections are 

 set side by side, the same series of numbers is used as in the 

 table -5 of sections from central Wyoming, and such layers as 

 are recognized as being equivalent are printed in heavy type. 



The Triassic of the west side of the Black Hills is made up of 

 barren red sandy clay. This grades into the green sandy clay 

 of the base of the Shirley, which for some eight to ten feet is 

 also barren. Here, however, Belemnites densiis begins to ap- 

 pear in great abundance. This clay is then the equivalent of 

 and like in texture to the Belemnites layer further west (No. 2). 

 The upper part of the layer may carry thin beds of limestone 

 as in the Inyan Kara Peak section. This is overlaid by a 

 layer of green clay with large limestone nodules (No. 4), 

 which vary in size from six inches to a couple of feet in di- 

 ameter. It is in and on just such nodules that Baptanodon 

 remains are found in the centre of the State. The layer was 

 everywhere + present both on the west and east sides of the 

 Hills. However, no trace of Baptanodon was found in any of 

 the exposures; but in the stone-pile of a yard on Miller Creek, 



» The east side sections are in manuscript; they were made by G. R. Wieland, and 

 verified by myself. 



2 Loomis, Bull. Amer. Museum. Nat. Hist., Vol. XIV, pp. 189-197. 



^ Last cit., p. 192. 



* Except in the Salt Creek section, which is an unusual one. 



