118 W. Cross — Igneous Hocks in Wyoming. 



due to original unevenriesses of the surface upon which the lava 

 was poured out, or to subsequent faulting, was not ascertained. 

 In the depression between this butte and the principal mesa 

 two or three small cones were seen, each with a vertical column 

 of rock rising from its apex. It is to be inferred that these 

 are volcanic plugs, similar to the Boar's Tusk, shortly to be 

 described. 



Occurrence of potash nitre. — On the eastern side of the 

 gap through which the top was gained, a cavity or recess with 

 overhanging roof, of irregular shape, several feet in length 

 and depth, was found in nearly massive rock. It was fully 

 exposed to the prevalent northwesterly breeze, and rain could 

 penetrate to the inner wall only when driven by very strong 

 winds. In this sheltered space was found a very unusual 

 mineral in a rather coarse, granular aggregate, and of sufficient 

 mass to allow collection of specimens several inches in diam- 

 eter. It seemed to occur as a partial crust to the cavity and 

 as a filling for irregular fissures which extended downward and 

 backward into the body of the rock. A columnar mass several 

 inches in diameter connected roof and floor of the recess at one 

 point where they were not less than one foot apart. Frag- 

 ments of rock were attached to the column, and its stalactitic 

 shape is probably an accident. This white granular substance 

 was analyzed by L. G. Eakins and found to be essentially 

 nitrate of potash. The exact result is given below : 



Analysis of nitre, etc. 



*Ilo/:::;:::::::::;::::: £*i }= 96 ' 40 nitre - 



CaO 1-09 \ 



SO, 1-59 J- = 3-31 s;ypsum. 



H/> -68.) 



c' :::;::::::::: :::::::: '11 \ = °- 16 halite - 



99-87 



It is regretted that the nature of this substance was not 

 recognized in the field, in order that closer observations of its 

 occurrence might have been made. As far as known there is 

 nothing to indicate the derivation of this nitre from organic 

 substances of any kind, yet such an origin is either evident or 

 assumed as probable for all other occurrences of natural nitrates 

 of which 1 find mention in manuals of mineralogy. This 

 occurrence is, however, entirely different from all others of 

 which notice has been found in literature. While extended 



* N 2 5 calculated for K 2 0. 



