344 PEOF. J. W. JUDD ON THE PEOPYLITES 



lavas, yet in the characters of their constituent minerals and in the 

 enclosures which these minerals exhibit they present the most 

 remarkable analogies with some of the older dioritic rocks. Tom 

 Rath also adopted the same view as Zirkel as to the close relations 

 existing between the propylites and plntonic rocks and their dis- 

 tinction as a group from the andesites. 



In the first edition of his very valuable work ' Mikroskopische 

 Physiographie der Massigen Gesteine,' published in 1877, Professor 

 Eosenbusch not only refused to accept the term " propylite " as dis- 

 tinctive of a group, but classed many of the rocks that had been 

 described under that name by other authors among the andesites. 

 In 1879, Dr. Doelter showed that the Hungarian rocks which pre- 

 sent the peculiar features held by von Richthofen and Zirkel to be 

 characteristic of the propylites, could be seen to pass by insensible 

 gradations into ordinary andesites * ; and the view that the propy- 

 lites were really altered forms of the andesites, was very forcibly 

 upheld by Eosenbusch in a review of Doelter's memoir, published 

 shortly afterwards f. 



In the same year Dr. "Wadsworth strongly insisted that the dis- 

 tinction between propylites and andesites could not be maintained 

 in the case of the North-American rocks J. 



Dr. Szabo of Buda-Pest, Dr. Anton Koch of Klausenburg, and 

 Dr. E. Hassak of Gratz, have all expressed the opinion .that the 

 propylites of Eastern Europe are really altered forms of the an- 

 desites. 



The publication in 1882 of Mr. George F. Becker's " Geology of 

 the Comstock Lode and the Washoe District '" marks an important 

 epoch in the history of the propylite controversy §. Mr. Becker, 

 while still continuing to classify the diorites and other plutonic rocks 

 as Pre-Tertiary, maintained that the propylites could not be regarded 

 as a distinct group of rocks, but only as a distinct "facies" or 

 " habitus " of the andesitic lavas. As the result of a microscopic 

 study of a large series of specimens obtained during the construc- 

 tion of the Sutro Tunnel, and the numerous deep workings of the 

 Comstock Lode, Mr. Becker was able to show how, by the gradual 

 alteration of their constituent minerals, the hornblende- and augite- 

 andesites could be seen to gradually acquire those peculiar cha- 

 racters which had been held to be distinctive of the propylites. 



Not less important as a contribution to this interesting question 

 is the very remarkable memoir of Messrs. Arnold Hague and J. P. 

 Iddings, " On the Development of Crystallization in the Igneous 

 Eocks of the Washoe District '*||. The authors of this memoir, 

 while fully accepting the conclusions of Mr. Becker that the pro- 

 pylites of the Washoe district are simply altered forms of the 

 andesitic lavas, went much further, and proceeded to show that the 



* Verhand. d. k.-k. geol. Keicbs. 1879, p. 27. 

 t Keues Jabrb. filr Min. &c. 1870, p. 648. 

 + Bull. Mils. Comp. Zool. vol. v. (1879) p. 285. 

 § United States aeol. Surv. Monograph iii. (1882). 

 11 Bull, of the U.S. Geol. Surv. No. 17 (1885). 



