Douglass : A Geological Reconnaissance. 273 



Campeloma harlo7Vionensis. 



Viviparus moniana'ensis. 



Goniohasis ? ortmaniii. 



Goniobasis silberlingi. 

 I had been much inclined to refer the beds to the Jurassic, but if 

 Professor Stanton is correct in referring them to the Lower Cretaceous, 

 it is exceptionally desirable that collections of dinosaur bones be made 

 from this formation, as the lower geological horizons from which these 

 remains have previously been obtained, represent a very limited por- 

 tion of dinosaurian life. 



The American Fork Beds. 



Overlying the red and somber clays and thin-bedded sandstones 

 above described, are clays, shales, and bedded sandstones, which, 

 until they are satisfactorily correlated, may be called the American 

 Fork formation, as they occur near the American Fork of the Mussel- 

 shell River. They partly, perhaps entirely, surround the dome-shaped 

 uplift of the underlying beds, and, of course, dip away from the center 

 of the uplift. Here the sandstones weather into ridges and the shales 

 into long depressions or ravines. The outcropping sandstones on 

 some of the ledges break into long regular slabs, which are sometimes 

 long enough for fence rails. The color of the shales comprises several 

 dark shades. I understand that some vertebrate remains have been 

 found in these beds. If this be true, they should be of special interest. 

 In the upper portion of the beds sandstone predominates. The beds 

 may or may not prove to be of Dakota age. The whole series is several 

 hundred feet in thickness. 



The Fort Benton Formation. 



The Fish- Creek Region. — The Fort Benton beds are well developed 

 in the region of Fish Creek. Immediately overlying the uppermost 

 sandstones of the preceding formation are shales and sandstones. In 

 the shales are brown concretions, in some of which large specimens of 

 Prionocyclus were found. At a higher level in a bank of dark clay on 

 Mud Creek, large ammonites, large specimens of Inoceramus (prob- 

 ably /. exogyroides Meek and Hayden), Scaphites, Faailites, and Ser- 

 piiliB were found. In the dark clays or shales there are harder, more 

 ferruginous bands. As the overlying Eagle sandstones are approached 

 the deposits become more arenaceous. Here the beds weather into 

 ravines between the sandstones below and above. 



