122 



GEOLOGY OF THE BLACK HILLS. 



is necessarily incomplete and wanting in absolute accuracy, but it is believed 

 to present the character and thickness of the Carboniferous strata with a 



fair amount of exactness. The exposures of 



^ the Potsdam were not sufficiently perfect for 



1 measurement. 



i 



a 

 o 



to 



Carboniferous. 



Feet. 



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1. Limestone, pink, impure and silicious, con- 



taining fragments of crinoid stems (So. 



1) exposed . . 20 



2. Limestone, white or gray (So. 2) 180 



3. Limestone, silicious, containing much flint 



and colored silicions matter ; has a brec- 

 ciated appearance (So. 3) 250 



4. Alternating limestones and calcareous sand- 



stones; yellow, reddish, white, and pink ; 

 near the base a marked stratum of deep 

 red, calcareous sandstone 10 feet thick; 

 the top beds a deep red sandstone, with 

 much lime in nodules or concretions 

 (lower part of ]STo. 4) . estimated . . 200 



5. Variegated sandstone, distinctly banded in 



strata of different colors, red, yellow, and 

 white (upper part of No. 4) 100 



Bed Beds. 



6. Eed clay, with some soft, red sandstone 100 



7. Purple limestone 25 



8. Eed clay and gypsum forming the Eed Val- 



ley 



g.S = 52 



+3 J2 i ■ ~ O 



.2 0= r? ki'3 



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rH ffl* M ^< Ifl 



In obtaining the above section, series of 

 partial measurements were made as follows: 

 Having measured the first section the can on 

 was followed down until the capping bed of 

 the section was seen to reach the creek, when 

 another section was made, and so on through the canon. 



The limestones were not found at any place to be fossiliferous, but the 

 different beds correspond closely in their lithological characters with the 

 Carboniferous as described in other parts of the Hills. No. 5 of the local 



