1 90 1.] Loomis, J^urassic Stratigraphy in Wyoming. I9I 



and underlies the Fort Pierre, I consider it the representative of 

 the Niobrara, although it is non-fossiliferous. A bed of gray sand- 

 stone comes next, making a prairie about three miles wide, so 

 that to estimate its thickness is difificult, though there can scarcely 

 be less than 300 feet. The sandstone furnished several badly 

 preserved fossils among which were Inoccrainus, Gryp/icB, and 

 ScapJiites 7uarreni M. & H. While the x\mmonites are described 

 as Fort Benton, inasmuch as I found the same at locality r mixed 

 with the Fort Pierre Gasteropoda and Lamellibranchiata, and 

 being strongly influenced by the stratigraphy, I am inclined to con- 

 sider the sandstone bed Fort Pierre. i\cross the sandstone the 

 Niobrara clay reappears, on its northern boundary nearly horizon- 

 tal, but on the southern side overthrust, so that the Fort Benton 

 lies inverted over the Niobrara. The Fort Benton dips 60° to the 

 south (strike N, 48° E.). The change to the vertical occurs in 

 the Dakota, which at this exposure (Carleton ridge) is only about 

 one-half its usual thickness. The Jurassic dips 80° N, but as 

 the Triassic is crossed the dip decreases to horizontal, changes 

 to south, and gradually increases to about 17° S., at which angle 

 most of the rocks, as far as the Prager anticline, dip. The 

 section goes only to Como Bluff but the rocks at Prager anticline 

 again show overthrust characteristics. 



Three sections of the Jurassic are shown in Plate XXVII, 

 Figs. I, 2, and 3, giving the details of the series of rocks on the 

 south side of Medicine anticline, and the north and south sides 

 of the Como anticline. These sections are also tabulated on 

 page 192" so that each layer can be traced in its variations across 

 the two anticlines. 



The base of the Jurassic I have located at the beginning of the 

 series of clays. The Triassic is a great bed of sandstones, usually 

 alternating red and gray. The first change from this to Jurassic 

 is a layer of brown clay (No. 2), always of considerable thickness, 

 and carrying Belemnites densus M. and B. curtiis L. in such abun- 

 dance that the ground is in many places so strewn with the shells 

 that one can scarcely step without treading on one. The layer is 

 widespread, occurring on Sheep Creek,' Medicine and Como anti- 

 clines, and is identical with Knight's No. 14," and the lower part 

 of Logan's No. 13.^ It is usually designated as the Belemnite layer. 



' The Sheep Creek exposures are 12 miles northeast of Bone Cabin Quarries. 

 = Bull. Geol. Soc. Amer., Vol. XI, p. 382. 

 ^ Kan. Univ. Quart., Vol. IX, p. 112. 



