﻿part 3] 



THE PSEUDOTACHYLYTE OF PARIJS. 



213 



(1) The absence of shearing - and cataclastic phenomena in the granite. 



This can only be accounted for by supposing the fractures to have 

 been produced by sudden snapping of the granite in response to a 

 sudden stress ; but how, unless there was long- continued friction, 

 could the quantity of fine dust necessary to fill the fissures be 

 supplied ? 



(2) The common occurrence of blind veins seems positively to exclude 



the possibility of long-continued friction ; the blind veins do not 

 differ in texture or composition from the others. 



VI. The Chemical Composition of the Pseudotachylyte. 

 (See also Appendix, p. 217.) 



When I first examined these rocks, I had no means of making 

 a chemical analysis of the material. Subsequently, when the 

 question of the origin of the pseudotachylyte was reopened, my 

 assistant, Mr. R. A. Page, kindly undertook to perform the 

 necessary analyses, and the figures given below are due to him. 

 In justice to Mr. Page, I must state that the work was performed 

 under very unfavourable conditions, with a deficient supply of 

 platinum vessels, with acetylene burners and a spirit blast-lamp 

 for ignition, and without reagents of special purity ; consequently, 

 it was not expected tbat a high degree of accuracy could be 

 attained. The summation of the analyses is low ; but, as we are 

 concerned rather with the general chemical character of the rock 

 than with the very precise determination of individual constituents, 

 the result has proved quite serviceable, and I desire to record my 

 great indebtedness to Mr. Page for his careful labour. The figures 

 are given in the first two columns below ; those in the third and 

 fourth columns refer to Backlund's analyses of black mylonite 

 and grey mylonite respectively, the minor constituents being 

 omitted : — 





16. 



n. 



HI. 



SiO„ 



62-03 



62-66 



65-75 



68-24 



Ti<X 



n. d. 



n. d. 



0-66 



0-01 



A1 2 0 3 



16-57 



16-26 



15-56 



16-08 



Fe?,0, 



2-51 



2-51 



0-64 



0-81 



FeO 



2-90 



2-89 



3-30 



2-20 



MgO 



0-39 



n. d. 



1-77 



0-40 



CaO 



3-39 



3-99 



3-75 



3-42 



Na.,0 



6-37 



5-88 



3-11 



3-34 



K.,6 



3-41 



2-75 



4-11 



3-99 



hIo- 



0-16 



| 0-96 



r o-08 



0-08 



h.;o+ 



0-72 



1 0-69 



0-83 



co 2 



o-oo 





0-74 



0-59 



Totals 



98-45 



97-90 













Ti0 2 , Zr0 2 , MnO, and P O, were present in small quantities, but were 

 not determined by Mr. Page. 



Q. J. G-. S. No. 287. e 



