144 STANTON & KNOWLTON — LARAMIE AND RELATED FORMATIONS. 



in character and thickness within short distances, but the fossiliferous 

 and overlying portions of the section may be described in general terms 

 as a series of variable sandstones, cla} 7 s, and coal beds exposed in low 

 hills and ridges with a dip of 9 or 10 degrees eastward at the base, but 

 decreasing in the upper portions to 5 or 6 degrees, which is about the 

 same as the dip of the overlying Wasatch beds. 



The character of the mollusks shows that the lower beds were mostly 

 deposited in brackish waters, but that there were alterations of fresh 

 waters in which the genus Unio thrived with an abundance of individ- 

 uals and great variety of species, and several fresh-water gasteropods 

 were common. Between the top of the massive sandstone and the Dino- 

 saur horizon there is a band filled with brackish-water fossils, including 

 Ostrea glabra, var. arcuatilis, Meek ; Anomia micronema, Meek ; Corbula un- 

 difera, Meek, and Modiola sp. The greater number of the Black Buttes 

 invertebrates, however, have been obtained from strata some 40 or 50 feet 

 higher, and consequently a little above the Dinosaur bed. Here there 

 is a band which in some places is about four feet thick, almost wholly 

 made up of shells. By far the most abundant species is Corbicida fracta, 

 Meek, and immediately associated with it are Corbicida occidentalis, M. 

 and H.; Neritina baptista, White; N. volvilineata, White, and Melaniawyo- 

 mingensis, Meek, all of which probably lived in slightly brackish water, 

 for this species of Melania has almost invariably been found associated 

 with brackish water or marine forms, although it belongs to a fresh- water 

 genus. At the base of this shell bed and immediately above a coal seam 

 Unio shells are abundant. These purely fresh-w T ater forms are found on 

 the slope mingled with the Corbicida shells, but all that were found in 

 situ were either at the base of or a few feet above the Corbicida bed. 



The Unione fauna is strikingly like that of the Ceratops beds in Con- 

 verse county, as the following list of species will show : 



Unio couesi, White. 

 Unio propheticus, White. 

 Unio aldrichi, White. 

 Unio proavitus, White. 

 Unio holrnesianus, White. 



Unio endhchi, White. 

 Unio cryptorhynchus, White. 

 Unio brachyopisthus, White. 

 Unio goniambonatus, White. 

 Unio danx, M. and H. 



Immediately above the Corbicula bed a band is locally filled with 

 Tidotomathompsoni and occasional Unios, and it is overlain by shales 

 containing Ostrea and Anomia in the lower part and the following species 

 above : 



Unio couesi, White. 

 Corbula undifera, Meek. 

 Corbula subtrigonalis, M. and H. 

 Cassiopella turricula, White. 



Goniobasis gracilenta, M. and H. (?) 

 Viviparus plicapressus, White. 

 Campeloma vetula, M. and H. 

 Campeloma multilineata, M. and H. 



