458 GEOLOGICAL SURVEY OF THE TERRITORIES. 



making this reference by the simihirity of one of the oysters to a Cre- 

 taceous species found in California, while the Anoinia likewise closely ' 

 resembled a Texas Cretaceous shell, described by lloemer under the 

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

 oyster. The two shells from nallville, however, I referred 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, ?) but because I was not aware at the time that the Hallville 

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

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

 laid down on any map 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 no other guide 

 than their aflinities, which would certainly jilace them in the Tertiary. 



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

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

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

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

 for 1,600 to 1,809 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 rocks 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 w^ell as to the present epoch, unless Leptesthes 

 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 



