﻿J. S. Diller — Peridotite of Elliot Co., Kentucky. 121 



hydrous minerals, and as R is composed of Ca, K 2 and Na 2 we 

 can assume the possible existence of the pure lime, potash and 

 soda compounds : 



CaAl 2 Si 10 O 24 +5H 2 O 



K 2 Al 2 Si 10 O 24 +5H 2 O 



Na 2 Al a Si 10 O 34 +5H a O 



The theoretical composition of an isomorphous mixture of 

 these three compounds, in the ratio derived from the analysis 

 of ptilolite, is given below in comparison with the analysis. 

 The molecular weight of the mixed EO molecule was calcu- 

 lated to be 66*92. 



Calculated. Found. Difference. 



Si0 2 69-86 70-35 + 0'49 



A1 2 3 11-87 11-90 + 0-03 



CaO 4-04 3-87 — 0*17 



K 2 2-95 2-83 - 0'12 



Na 2 0-80 0-77 - 0-03 



HO 10-48 10-18 - 0-30 



100-00 99-90 



The rare mineral milarite, although possessing a ratio RO : 

 Al 2 3 =3 : 1, may yet be compared with ptilolite on account of 

 its exceedingly high percentage in silica. Its formula is HK 

 Ca 2 Al 2 Si 12 O 30 , requiring 72*66 per cent Si0 2 . 



Art. XII. — Notes on the Peridotite of Elliot County, Kentucky ; 

 by J. S. Diller. 



Several years ago Professor A. R. Crandall discovered two 

 dikes of an interesting eruptive rock in eastern Kentuck}^, 

 about seven miles southwest of Willard. The position of these 

 dikes is well shown upon Professor Crandall's geological map 

 of Elliot County. 



A preliminary examination of the rock under the microscope 

 revealed the fact that it belongs to the peridotites. These 

 rocks are considered by most petrographers as eruptive, but 

 there are others who regard them as of doubtful origin. One 

 of the latest writers on petrography* divides rocks into two 

 great classes: (1) those resulting from the accumulation of ma- 

 terial transported from lower to higher levels (Anogene), and 

 (2) those resulting from the accumulation of material trans- 

 ported from higher to lower levels (Katogene). The first 

 group includes rocks of eruptive origin, while the second con- 



* Elemente der Lithologie von Dr. Ernst Kalkowsky. 1886. 



