478 PROCEEDINGS OF THE ALBANY MEETING 



The following paper was presented in abstract by W. B. Scott. 



A DEPOSITIONAL MEASURE OF UNCONFORMITY 

 BY CHARLES R. KEYES 



The paper is printed as pages 173-196 of this volume. 

 The two follow ino- papers were read by title : 



COMPARISON OF STRATIGRAPHY OF THE BLACK HILLS WITH THAT OF THE 

 FRONT RANGE OF THE ROCKY MOUNTAINS 



BY N. H. DARTON. 



[Abstract'\ 



After several years of detailed investigation of the stratigraphy of the Black hills 

 in South Dakota and Wyoming, a preliminary examination has recently been made 

 of the region southwest to and along the front ranges of the Rocky mountains across 

 Wyoming and Colorado. Tlie Black hills are due to a local expansion of a branch of 

 the Laramie range, hut the connection underlies a country in great part covered by 

 Tertiary depo.sits. In the vicinity of Hartville, about 125 miles southwest of the 

 Black hills, there is a local uplift on this line, affording extensive exposures of 

 formations from the crystalline schists part way up the Mesozoic column. The 

 stratigraphy is here very similar to that of the Black hills, and all the principal 

 formations from Lower Cretaceous sandstones to the Lower Carboniferous lime- 

 stone can be distinctly recognized. Along the flanks of the Laramie range and 

 southward into Colorado the formations present considerable change, but numerous 

 features of close relationship were ohserved. In the fine sections at Morrison, west 

 of Denver, there was found an extension of the Purple (Minnekahta) limestone of 

 the Black hills having precisely similar stratigraphic relations in the Red beds and 

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

 preserved. The limestone was traced south for a considerable distance, and 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 

 INIorrison affords the means for a precise correlation with the Black Hills region. 

 The underlying mass of coarse sandstone against the crystalline rocks represents 

 portions or perhaps all the Carboniferous formations of the Black hills. The Red 

 beds overlying this Minnekahta limestone at Morrison are gypsiferous shales 

 similar to those of the red valley encircling the Black hills. The Morrison forma- 

 tion lying next above is, as previous observers have pointed out, the equivalent of 

 the Atlantosaurus (Beulah) shales, while the marine Jurassic, which was traced as 

 far south as the Hartville region, is lacking in the Morrison section. The lower 

 Cretaceous sandstone in the Black hills has not been recognized in Colorado. The 

 Benton formation presents the same three divisions through the Black Hills region 

 as were determined by Gilbert in southern Colorado. In the valley of the Purga- 

 oire, in southern Colorado, the Red Bed series is represented by red sandstones 

 of moderate coarseness, in the upper bed of which was discovered a bone of a 

 Bolodont, which is thought to be of Triassic age. The overlying series of gypsum, 

 limestone, and shale yielded no fossils, but probably comprises a representative of 



