486 REPORT UNITED STATES GEOLOGICAL SURVEY. 



acter of the limestones is subject to local variation, but to just what ox- 

 tent those changes are manifested will require much patient research to 

 determine. In the aggregate, this division attains a thickness of 1,000 

 to 2,000 loot, approximate. 



In the Mount Putnam Eidge the basis rocks show a heavy ledge of 

 rough-weathered, buff-gray siliceous limestone, containing a few obscure 

 fossils, crinoidal remains, and a Ilcmipronitcs. This is succeeded by a 

 heavy bed of light-gray, cherty, rough-weathered limestone passing up 

 into dark bluish-gray rather even-bedded limestone, with black chert, 

 charged with a large Zaphrentis, Spirifer, &c. In the vicinity of the out- 

 crop of the latter deposits, in the little hill-environed basin of Boss Fork, 

 my notes make mention of a considerable deposit of conglomeritic mate- 

 rials, chiefly composed of light-gray limestone pebbles, with some of quartz, 

 and apparently interlaminated with buff, shaly limestone layers, in which 

 occur fragments of an Avieidopccten. The relations of this deposit to 

 the apparently overlying beds above referred to is not clearly indicated, 

 and it is mentioned here that attention may be called to the subject for 

 the future settlement of any doubts that may exist as to its relations to 

 these rocks, with which it seems to constitute a conformable member. 

 The beds above mentioned belong to the lower division of the Carbonif- 

 erous, and at one point in this neighborhood Professor Bradley discov- 

 ered in these rocks a peculiarly Lower Carboniferous fauna, many of 

 whose abundant minute forms Mr. Meek found to be specifically identi- 

 cal with those which characterize the Warsaw beds in the Upper Missis- 

 sippi Valley. All these deposits dip to the eastward, but in the opposite 

 side of the synclinal within the area of a basin at the head of one of the 

 tributaries of the Portneiif, they have been denuded and concealed by 

 late accumulations, only the Upper Carboniferous horizons being seen at 

 this point. 



To the northeast, however, in the Blackfoot Eange, the lower forma- 

 tions are extensively displayed. Their occurrence in this quarter is also 

 accompanied by evidences of much disturbance, the strata are folded 

 and, perhaps, faulted, on which account, notwithstanding the exception- 

 ably good exposures so prevalent here, it will require much time to ac- 

 quire familiar acquaintance with the stratigraphic details of the series. 

 These inferior limestones reach a thickness of several hundred feet, per- 

 haps 2,000 feet, including quartzitic horizons and red-stained siliceous 

 deposits in positions below well-marked Lower Carboniferous horizons. 

 Paleontologically, horizons in these cherty limestones are characterized 

 by associations of fossils which have intimate likeness to certain Lower 

 Carboniferous formations in the Upper Mississippi region. 



As at the locality in the Mount Putnam Eidge, we here find, in the 

 vicinity of Station X, an eminently Warsaw inolluscan fauna. Else- 

 where the lithological, as well as the paleontological, resemblances 

 of certain horizons amount to almost absolute identity with the Keokuk 

 formation, as developed in the Western States. At Station VII, in a 

 dark bluish-gray cherty limestone, with lighter colored shaly partings 

 crowded with corals, Polyzoa, &c, a veritable fish-bed occurs, from 

 which were obtained representatives of the Selachian genera Cladodus, 

 Deltodus, Selodus (Lophodus), Petalodus, Antliodus. As is well known, 

 one of the above-named genera, Antliodus, is restricted to Lower Car- 

 boniferous formations, while all the other forms are closely allied to, if, 

 indeed, they prove not to be identical with, species peculiar to the lower 

 divisions of this series of formations in the Mississippi Valley. The 

 affinities of the fish-remains do not indicate a later date for the beds in 

 which they occur than the Keokuk formation. Hence, so far as the evi- 



