MINGLING OF MESOZOIC AND PALEOZOIC PACIKS. 300 



found a close correspondence with the section made by myself on Belt 

 creek. Fossils collected by Davis from these same shales, supposed by 

 him when in the field to be Jurassic, were reported to be Spergen hill 

 types by Professor Whitfield; this places them in the lower Carbonifer- 

 ous. The list given by Professor Whitfield is as follows : 



Rhynchonella mutata, H. Terebratula turgida. 



Proiluct i is tenuicostdtus, H. Allorisma, sp.? 



Athyris trinucleata, H. IAngula, sp. ? 



Eumevria verneuiliana. Stictopora, sp.? 



These species and those enumerated above do not include a single 

 characteristic Jurassic type. Notwithstanding the wide range of many 

 of the species, and in general of the molluscan fauna so abundant in the 

 Carboniferous, rendering such paleontologic evidence by itself of little 

 value in determining exact horizons, it is noteworthy that fossils charac- 

 teristic of the lower Carboniferous should be found in beds formed during 

 the very close of the Carboniferous period. It should be noted in this 

 connection that fossils from a very much lower horizon in the section 

 made by Professor Davis are described by Whitfield as upper Carbonif- 

 erous. The stratigraphic position and lithological character of the lime- 

 stones and shales from which the fossils collected by myself were obtained 

 correspond closely to those of the beds found in southern Montana to 

 be characterized by an abundance of Jurassic fossils.* Such a decided 

 change in the upper part of the Carboniferous from that observed else- 

 where indicates a local modification of prevailing conditions and near- 

 lie--, ( .f a shore line. 



The Jurassic. — This shaly series is overlain by a bed that is character- 

 istic of the Jurassic throughout central Montana, in its lower portion it 

 is frequently a good crystalline limestone, passing gradually into a coarse 

 sandstone, frequently a conglomerate closely resembling the Dakota but 

 carrying Large numbers of Jurassic shells in both the sandy and limestone 

 portions of the bed (number of the section). 



The belt creek section gives a total thickness of 538 feet of beds be- 

 tween the white limestone of the Carboniferous and the Jurassic. 



The Kootanie. — Overlying the Jurassic conglomerate bed (number 6 of 

 the section ) there is a series of rather thinly bedded stands! ones of vary- 

 ing degrees of coarseness and induration. Near the mountains these 

 rocks are ferruginous and bright ra] in color, but farther away from the 

 uplift they are white and contain intercalated beds of shale and ferrugi- 

 nous sands. A 5-foo1 bed of dense yellow sandstone, quite impure and 

 argillaceous, forms a recognizable division of this sandstone series. The 



• Cf. W. H. Weed, Cinnabar and Bozeman Coal Fields: Bull. Geol. Soc. Am., vol. 2, 1801, pp 



XI. II -I'.i 1 1 . Geoi . Soc. \m.. Voi . 8, L891, 



