OF THE WESTEKN ISLES OF SCOTLAND. 



II. Pkeviotjs Literature. 



343 



In his great work on the Geology of Hungar}-, Beudant, as early 

 as 1822, distinguished a series of rocks presenting very well-marked 

 features, to which he gave the name of " porphyres trachytiques "*. 



In 1860, Baron von Richthofen proposed to separate these rocks 

 from the ordinary trachytes (andesites) of Hungary and Transyl- 

 vania under the name of " greenstone-trachytes " t; and this term — 

 indicating their analogies both with plutonic and with volcanic 

 rocks — was very generally accepted by von Haiier, Stache, and the 

 other geologists of Austria.- 



In 1868, however, von liichthofen was led by his study of the 

 volcanic rocks of California and Nevada to abandon the term 

 " greenstone-trachyte " in favour of that of " propylite ;" he was 

 induced to make this change froni his conviction that, in Hungary 

 and Transylvania, as well as in the western districts of the North- 

 American continent, the rocks in question were the earliest 

 erupted of the whole series of Tertiary lavas J. 



In 1875 the late ]\Ir. Poulett Scrope, who was well acquainted with 

 the Hungarian rocks, pointed out to me the close similarity between 

 many of the features exhibited by the volcanic rocks of that country 

 and those which I had described in the Western Isles of Scotland. 

 In consequence of his advice, and with his friendly assistance, I 

 visited Hungary and Transylvania in that year, and some of the 

 general results of the comparisons then made were submitted to this 

 Society shortly afterwards. The conclusion at which I arrived with 

 respect to the " greenstone-trachytes *' or "propylites" of Eastern 

 Europe was that, while they have intimate relations on the one 

 hand with the andesites, and on the other hand with the diorites 

 of the same district, yet many of their peculiarities are certainly 

 due to their having undergone great alteration, especially in con- 

 seciuence of having been acted upon by acid vapours §. 



The name " propylite," as distinctive of a well-marked group of 

 rocks, was adopted by Mr. Clarence King and other members of the 

 United-States Geological Survey engaged in the exploration of the 

 Western Territories, and the term thus became familiar to all stu- 

 dents of American geological literature, while its use in Europe still 

 continued to be very restricted. 



In 1876, however, Prof. Zirkel published the results of his micro- 

 scopical study of the North-American rocks ; and in this work he 

 endeavoured to define the particular characters which seemed to 

 justify the retention of the " propylites " as a distinct type of 

 rocks ||. Dr. Zirkel pointed out that, while in their geological re- 

 lations the propylites are clearly associated with the Tertiary 



* Voyage Mineralogique et Geologiqiie en Hongrie, tome iii. p. 344. 

 t Wien. Geol. Vcrhancllungcn, xi. (1«60) pp. 91-04, and Jahrb. k.-k. geol. 

 Kt'iclisanstaU., Wien, xi. (18(50) pp. liA-'27iJ. 



I Mem. California Acad, of Sci. vol. i. (1868). 

 i^ Q. J.G.S. vol. xxxii. (US7()) p. 208. 



II Microscopic Tetrograpliy, vol. vi. of the U S. Geol. Expl. of tlic Fortieth 

 Parallel (1870), pp. 110-121. 



2c2 



