UPPER RED BEDS OF THE BLACK HILLS 38 1 



The analyses show traces of chlorine. Probably this is pres- 

 ent as common salt, which, in spite of its solubility, may repre- 

 sent salt deposited in the red beds during their formation. No 

 beds of rock salt have been found in the red beds of the Black 

 hills, but a local accumulation is suggested by a salt spring in 

 the red beds about three miles northeast of Cambria, Wyo. An 

 analysis of this water by Mr. Steiger showed : 



Grams per Liter. 



CaO . - . . . 1.960 



MgO -.---. .448 



K2O ------ none 



NazO 27.334 



SO3 - - - - - - 3-556 



CI --.... 31.479 



Br ----- - none 



I ...... none 



64.787 

 Less 0=C1 - - - - - 7.094 



57-693 



= 51.582 grams of NaCl per liter. 



DISCUSSION. 



Red beds in general are well known to be colored by ferric 

 hydrate or ferric oxide, but conditions that determine the forma- 

 tion and deposition of red pigment are various. Red beds have 

 accumulated at different times and in different localities, under 

 different conditions. This study was undertaken with the pur- 

 pose of seeking evidence for the origin of the color of the red 

 beds of the Black hills. 



The history of these rocks is intimately connected with the 

 history of the entire series of red beds of the central West, and 

 a complete treatment of the subject is impossible without the 

 accumulation of more facts, concerning the general geology of the 

 Rocky mountains and adjacent regions, than are now known. 

 Nevertheless the red beds of the Black hills constitute an isolated 

 mass, and it is thought that an inquiry into the cause of their 

 color, based on their description, will not be inappropriate. 



TJieories for the origi?i of the color of red beds. — One of the most 

 obvious origins of red rocks is that they are formed by the dis- 



