458 GEOLOGICAL SURVEY OF THE TEEEITORIES. 



making tliis reference by tlie similarity of one of the oysters to a Cre- 

 taceous species found in California, while tlie Anomia likewise closely 

 resembled a Texas Cretaceous shell, described by Eoemer under the 

 name of Ostrea anomioeforniis, which certainly seems not to be a true 

 oyster. The two shells from Hallville, however, Lreferred to the Eocene, 

 not only because they are very closely allied to Eocene brackish-water 

 forms from the Paris Basin, (peculiar depressed and elongated forms of 

 Corbicula, 1) but because I was not aware at the time that the Hallville 

 mines occur in the same formation as the Point of Eock beds, nor even 

 within fifty to seventy-five miles of the same locality. Hallville is not 

 laid down on any maj) I have even yet seen, and I was entirely ignorant 

 of its position, both geologically and geographically, with relation to 

 Point of Eocks ; and as the species were new, I had ho other guide 

 than their affinities, which would certainly place them in the Tertiary. 



On visiting these localities, however, last summer, I was somewhat 

 surprised to find that the Hallville mines are only some seven or eight 

 miles from Point of Eocks, and belong to the same geological formation. 

 A carefal examination also soon rendered it evident that all of the rocks, 

 for 1,600 to 1,800 feet or more above the Hallville coal-beds, up to and 

 including the stratum in which we found the large reptilian remains at 

 Black Butte, and for even a little greater thickness below the Hallville 

 horizon, certainly belong to the same group or series of strata; and that 

 fresh and brackish-water types of fossils occur along with salt-water 

 forms, at all horizons, wherever we found any organic remains through- 

 out this whole series. 



As we discovered in these roTsks between three and four times as 

 many species of fossils as had been previously known from the same, it 

 becomes a matter of some interest to consider the whole with regard to 

 their bearing on the question as to the age of the group. The reptilian 

 remains found at Black Butte, near the top of the series, have, as else- 

 where stated, been investigated by Professor Cope, and by him pro- 

 nounced to be decidedly Dinosaurian and, therefore, indicative of Cre- 

 taceous age ; on the other hand, the fossil plants from the same beds 

 have been studied by Professor Lesquereux, who informs me that they 

 are unquestionable Tertiary types. My own investigations having been, 

 confined to the invertebrates, it is of these chiefly that I will speak here. 

 In the first place, it will be seen that all of these yet known belong to a 

 few genera of mollusks, represented by some twelve or fourteen species. 

 And just here it may be stated that, although partly committed in favor 

 of the opinion that this formation belongs to the Cretaceous, and still 

 provisionally viewing it as most probably such, I do not wish to dis- 

 guise or conceal the fact that the evidence favoring this conclusion to 

 be derived from the mollusks alone, as now known, is by no means strong 

 or convincing. The genera are probably all common, both to the Cre- 

 taceous and Tertiary, as well as to the present epoch, unless LeptestJies 

 and Veloritina, which have been separated subgenerically from Corbicula^ 

 may be distinct genera, the European representatives of these being 

 mainly, if not entirely, Tertiary forms, while they do not appear to in- 

 clude living species. Goniohasis is also not known in either Cretaceous 

 or Tertiary rocks of the Old World ; but then it is an American type, 

 greatly developed among our existing mollusca, as well as in the far 

 western Tertiary rocks, and we can scarcely doubt that it will be found 

 in unquestionable Cretaceous beds there, even if some of the imperfect 

 specimens already known from the same are not such. It should be 

 remembered, however, that even the specimens I have referred to this 



