112 GEOLOGY OF THE BLACK HILLS. 



ing series, and above this fossiliferous stratum the same series continues for 

 over 200 feet. The fossils, mere fragments, are indeterminable; but among 

 them are minute gasteropods and small Spirifer-like shells. 



Above the alternating series, and therefore, according to our classifi- 

 cation, above the Carboniferous, there follow in ascending order, first, 75 

 to 100 feet of red arenaceous clay; second, io to 30 feet of purplish im- 

 pure limestone; and, third, 200 to 250 feet of red clay with gypsum. The 

 arenaceous tendency of the lower clay allies it to the sandstone at the top 

 of the alternating series and makes it difficult to draw the line of separation 

 even here ; but, all things considered, the division is more easily made at this 

 point than elsewhere. Limestone and sandstone are the characteristic 

 rocks of the Carboniferous throughout the northwest region; and regarding 

 only lithological evidence, it seems proper to make the separation where 

 the sandstone and limestone cease and the clay begins. Nevertheless in 

 Southern Colorado the Carboniferous is known to include in its upper 

 part large deposits of gypsum and associated beds of a deep red color, and 

 the same thing may possibly occur in the Black Hills. 



In 1857 Dr. Hayden found a few fragments of fossils in the Hills 

 which he recognized as identical with forms from western Kansas, which 

 had been studied by Mr. Meek and himself and referred to the Permian. 

 The rock in which they were found was a bowlder and the material was 

 not seen in place, but the indication that the Permian is contained in the 

 Black Hills section may furnish a cue by suggesting a comparison of the 

 doubtful beds with the nearest rocks for which the title Permian has been 

 claimed. 



Dr. Peale has examined in Colorado, on the Grand River, etc., certain 

 strata between the Coal Measures and Triassic which Professor Lesque- 

 reux decided from certain fossil plants found therein to be of Permian 

 age. Dr. Peale describes the series in words that will apply almost as 

 well to the lower part of the alternating series of the Black Hills, viz, 

 "variegated strata, yellow, pink, and cream colored shales and limestones, 

 subject to so much change that it was impossible to make any continuous 

 section." Similar thin-bedded deposits are also described by him in his 

 report for 1873, and he has regarded these also as of Permian age. 



