446 GEOLOGICAL SURVEY OF THE TERRITORIES. 



were seen, presenting a curious and puzzling appearance. They bad 

 grown crowded together by thousands, beak downward: while, in most 

 cases, the shell itself was dissolved away, leaving only the internal casts, 

 often 12 to 13 inches in length and only about 2 inches in breadth, 

 standing side by side, with their longer diameters at right angles to 

 the plane of the bed in which they were enveloped. At first it was 

 rather difficult toi comprehend what they could be, but on drawing some 

 of them that were loose from the cavities they were found to be the 

 internal casta of this peculiar oyster, showing the muscular scars quite 

 distinetly. In a few instances, however, some of these specimens also 

 retain the shell itself entire. 



The highest horizon in this great series of beds at which fossils were 

 seen in situ was in division 23 of the section, (fourth ridge.) Hei^e we 

 found in a light- grayish, soft sandstone numerous casts and broken 

 shells of a large Iiwceramus, with fragments of Ostrea and casts of a 

 Cardium. The T>ioceranius found here is a suborbicular, rather com- 

 pressed or moderately convex species, with a rather short hinge and 

 regular concentric undulations. It agrees well with Upper Missouri 

 specimens we have always referred to I. nebrascensis^ Owen, from the 

 Cretaceous, exceiJting that none of the specimens found are quite so 

 large as Owen's type; the size being about intermediate between 1. 

 Sagensis, and I. nebrascensis, Owen, which, however, may be only 

 varieties of one species. The fragments of Ostrea and casts of Cardium 

 found in the same association were too imperfect for satisfactory identi- 

 fication, but seemed to be very like forms found far below this horizon 

 in other beds. 



Along a slope formed by division 25 loose fragments of Ostrea were 

 observed, that appeared to be the same form found associated with the 

 Inoceramus and Cardium, in division 23, but none were seen in place. 



Beyond this, toward Echo Canon, as we ascend in the series the same 

 light- grayish colors prevail in the sandstones and intercalated beds of 

 conglomerate, for perhaps five or six hundred feet or more before we 

 come to the great brownish conglomerate of the canon. These lighter 

 colored sandstones, however, are coarser and less coherent than most of 

 those below the division 26. We looked carefully for fossils in these 

 beds, but found no traces of organic remains of any kind ; and, judging 

 from the coarseness of the material, it is proba]3le that it was rapidly 

 deposited during the prevalence of physical conditions unfavorable to 

 animal life. 



The same was also evidently the case, even in a far more marked de- 

 gree, during the deposition of those huge, massive beds of brownish 

 conglomerate, at Echo Caiion, (divisions 29 to 31, inclusive, of the sec- 

 tion,) which are so coarse as to present the appearance of consolidated 

 drift. These beds are mainly composed of water-worn rocks of every 

 size, from that oi' small pebbles to bowlders from 6 to 10 inches in 

 diameter, the larger sizes more frequently predominating. The inter- 

 stices are filled with arenaceous matter, and the whole firmly cemented 

 together. So far as examined, near the mouth of the caiion, a large ma- 

 jority of these pebbles and bowlders were found to be very hard, light- 

 grayish siliceous rock, apparently metamorphosed sandstone, though a 

 few of igneous origin were occasionally seen. The whole formation is 

 so massive that it would often be difiicult to see in it any evidences of 

 stratification, if it were not for occasional seams and lenticular bodies 

 of intercalated sandstone along certain horizons. These have a deep 

 reddish-brown color, and, as they are liable to weather out, where ex- 

 posed, they leave lines of cavities that impart to the surface of precip- 



