190 1.] Loomis, y^urassic Stratigraphy in Wyoming. I 93 



On the surface of this, in Bone Cabin Draw, is found a one-foot 

 bed of limestone (No. 3) made up mostly of iVucu/as,^ with 

 occasionally a Tancredia and Ostrea. The band is not continu- 

 ous, but similar layers at the same horizon occur both on Sheep 

 Creek and in the Freezeout Hills. 



No. 4 is a purplish clay with large limestone nodules scattered 

 through it. It is in or on these nodules that the specimens of 

 Baptanodon are found. That of the American Museum was 

 found at locality b, at the foot of Bone Cabin Draw. It seems 

 best to confine Marsh's^ term, Baptanodon beds, to this layer 

 instead of designating the wliole lower Jurassic by that term. 

 The bed is universally present in neighboring localities; and is 

 Knight's 12 and the upper part of Logan's 13. 



No. 5, green sand shale, is local. 



No 6, sandstone. This first sandstone bed seems to be widely 

 distributed, and marks the beginning of a series of alternations 

 between sandstone and clay. The clays are variously and 

 brightly colored and often designated as the ' variegated clays.' 

 The layers from 6 to 20 inclusive form a series of variegated beds 

 in which there may be eight sandstone layers or only three. Very 

 few of the clays seem to form wide horizons. Inside of a quar- 

 ter of a mile I have seen three of. the sandstone beds unite into 

 one thick sandstone, the intervening clays being pinched out. 

 These indicate a period of shallow water in which there were con- 

 tinually changing currents, so that deposits from any given source 

 are laid down first in one place, later in another. In the Bone 

 Cabin section there are 120 feet of these variegated clays, and 

 it is somewhere in these layers that the change from marine to 

 brackish (or freshwater) deposits occurs. In the Como section 

 there is a 28 foot bed of sandstone, corresponding apparently 

 with No. 13, in which a Dinosaur quarry (12) is located. This 

 bed seems to represent the beginning of the freshwater (or brack- 

 ish) series, and as such is the first member of the Como stage 

 (Atlantosaurus beds). This sandstone (No. 13) is variable in 



' At the foot of Bone Cabin Draw, locality h^ were found in this layer Nucula nov. sp., 

 Tancredia inornata^ Avicula mucronaia, a.nA Ostrea strigileciila. A similar band near 

 Sheep Creek furnished all of the above with also Cardioceras cordi/oriiiis M., and Pseudo- 

 juonotis curia ; see also Logan's No. 13, which furnished some of these and several other 

 forms. 



^ Sixteenth Ann. Rep. U. S. Geol. Surv., 1896, p. 145. 



{^Juue, igoi.] 13 



