﻿198 



PROF. S. J. SHAND ON 



[vol. lxxii, 



10. The Pseudotachylyte of Parijs (Orange Free State), 

 and its Relation to ' Trap-Shotten Gneiss' and 'Flinty 

 Crush-Rock.' By S. James Shand, D.Sc, F.G-.S., Pro- 

 fessor of Geology in the University of Stellenboseh. (Read 

 March 22nd, 1916.) 



[Plates XVI-XIX.] 

 Contents. 



Page 



I. Introduction 198 



II. Occurrence in the Field 199 



III. Microscopic Characters of the Pseudotachylyte 206 



IV. The Case for the Igneous Origin of the Veins 208 



V. Comparison of the Pseudotachylyte with ' Trap-Shotten 



Gneiss ' and ' Flinty Crush-Eock ' 209 



VI. The Chemical Composition of the Pseudotachylyte 213 



VII. The Case against an Igneous Origin . 215 



VIII. Conclusion 216 



• IX. Literature 217 



Appendix (Chemical Analyses) 217 



I. Introduction. 



In the year 1913 I received from a former student of mine, 

 Mr. P. H. S. De "Wet, a consignment of rock-specimens from the 

 neighbourhood of Parijs (O.F.S.). Among these were many pieces 

 of a dense black rock, which, I was informed, occurs very abundantly 

 in veins and networks in the granite. The characters of this rock 

 seemed so remarkable that I took an early opportunity of visiting 

 Parijs myself, in order to study the phenomena in the field. As 

 a result of my observations, I formed the opinion that the black 

 veins were intrusions of basic magma which had entered the granite 

 by a process of stoping, accompanied by corrosion and solution ; 

 and a paper embodying this conclusion was communicated to the 

 Geological Society in November 1914, an abstract of it appearing 

 in the Proceedings of the Society for that month (No. 964). After 

 the manuscript had left my hands, I became aware for the first time 

 of the work of Sir Thomas Holland and his colleagues of the 

 Geological Survey of India on the ' trap-shotten gneiss ' of Salem, 

 Madras, and I could not fail to be struck by the resemblance 

 between some of the phenomena there described and those observed 

 by me. My attention was next turned to the ' flinty crush-rocks ' 

 of the Cheviot Hills and other parts of Scotland, which were also 

 at one time held to be of igneous origin. By the kindness of 

 Dr. Flett, the late Dr. Clough, and Mr. E. B. Bailey, I was enabled 

 to study hand-specimens and sections of a large number of these 

 rocks ; and although, on comparing them with my own material, 



