BESUME OF LITEEATUKE. 101 



pink, and lilac. In this zone gypsum and brown earthy limestone are common." 

 (Page 36.) 



The Wyoming formation is succeeded bj-- the Morrison, consisting essentiallj^ of 

 fresh-water marls, and having an average thickness of about 300 feet. Its upper 

 limit is sharply defined by the Dakota sandstone. Its Mesozoic age is positively 

 determined by its contained saurian remains, and it is referred to the Jurassic. The 

 age of the Wyoming formation is assigned, on somewhat indirect and conflicting 

 evidence, to the Triassic. 



The Wj'oming formation is thought to overlie the Fountain formation described 

 in the publication previously discussed, which is referred to the Carboniferous, and 

 on this account a new name was given to the Wyoming beds. It is not improbable 

 that the greatly varying thickness of the Wj'^oming foi'mation in the Denver Basin 

 may be due to the presence of local undifferentiated fi-agments of the Fountain series. 

 The same suggestion is made by Emmons on page 19 of the monograph. 



In 1901 Darton " read a paper before the Geological Society of America entitled 

 "Comparisons of Stratigraphy of the Black Hills with that of the Front Range of 

 the Rocky Mountains." This paper was never published except in abstract, in which 

 form it appeared in the bulletins of the society and in Science. Speaking of the fine 

 sections at Morrison, west of Denver, he says: 



"There was found an extension of the Purple (Minnekahta) limestone of the 

 Black Hills, having preciselj' similar stratigraphic relations in the Red Beds and 

 containing some of the same Permian fossils, although these are scarce and not well 

 presei'ved.' The limestone was traced south for a considerable distance, ^.nd found 

 to merge into a sandy bed, which was finally lost in the great mass of coarse, red 

 deposits in the vicinity of the Garden of the Gods. Its very distinct occurrence at 

 Morrison afl:ords the means for a precise correlation with the Black Hills region. 

 The underlying mass of coarse sandstones against the crystalline rocks represents 

 portions, or perhaps all, of the Carboniferous formations of the Black Hills. The 

 Red Beds overljang this Minnekahta limestone at Morrison are gypsiferous shales, 

 similar to those of the red valley encircling the Black Hills." 



The geologic position of the horizon containing Permian fossils mentioned by 

 Darton is evidently in the Wyoming formation, and his characterization of the over- 

 lying beds as gypsiferous shales would indicate that it was in the upper division, from 

 200 to 300 feet below the top. Darton's correlation once accepted, the Paleozoic 

 age of nearly the whole of the Red Beds of this area would be demonstrated, the 

 Triassic being absent altogether or represented by a few hundred feet below the 

 Morrison beds. 



However, the character of the fossils upon which this correlation is based is 

 not stated, so that it is impossible to pronounce upon the weight which should 



aGeol. Soc. America, Bull., vol. 12, 1901, pp. 478-479. 



