The Nomenclature of the Keratophyres. 347 



signification, of the original name, and the individuality of the typo 

 rock. It must be conceded that this is the ultimate fate of the 

 majority of rock names as at present constituted : almost every 

 investigation results in the discovery of rocks differing by little or 

 by much from established types, it adds one or more links 

 to the chains connecting the latter, until finally a gradation from one 

 to the other is found to exist. 



It is thus useful and ne(;essary occasionally to look back in order 

 to see how the significance of particular rock names may have 

 changed, and to what extent original definitions must be modified 

 to conform to iucreased knowledge arising from more recent 

 discoveries. 



Withia recent years the Spilitic Suite of rocks has received almost 

 general recognition as a suite distinct from others in respect of 

 peculiarities of chemical and mineral composition, and in the mode 

 of formation of its members. This distinct individuality is most 

 marked in the case of the spilites, the basic members of the suite, 

 but is apparent also in the intermediate and acid members, the 

 keratophyres and quartz-keratophyres respectively. In spite of 

 iuteresting problems concernuxg the petrogenesis of these rocks, 

 they receive but scanty attention in our standard textbooks. Thus 

 Hatch, ^ when describing hypabyssal felsites is content to insert 

 " keratophyre " in brackets after the name soda-fclsite. Harker ^ 

 is hardly more explicit, though mention is made of the fact that 

 " ceratophyres " are sometimes intrusive, sometimes extrusive, 

 and consist mainly of soda felspars, with little or no quartz — a 

 definition which can scarcely be described as explicit. So the inquirer 

 has to search through contemporary geological literature to discover 

 the exact meaning of this name. The most useful account of these 

 rocks is that of Cox,^ in a short paper read before the British 

 Association in 1913, an account which has not yet been amplified, 

 however, although it contains many interesting suggestions. Apart 

 from this, much useful information can be gleaned from the published 

 accounts of the igneous rocks of various parts of Wales, Devon 

 and Cornwall, and Scotland. Among other British writers Cox, 

 Dewey and Flett, Hatch,. Jevons, Teall, and Thomas have used 

 the word, but by no means always with the same meaning. 

 The marked difference of opinion concerning the application of the 

 names " keratophyre " and " spilite " has led the writer to attempt 

 this review. 



II. Historical. 



As long ago as 1874 Giimbel ^ introduced the name keratophyre, 

 which he applied to rocks sometimes undoubtedly intrusive in the 



^ Hatch, Text Book of Petrology, part i, Igneous Rocks, 1913, p. 223. 



^ Harker, Petrology for Students, 5th ed. , p. 117. 



* Cox, Bep. Brit. Assoc. Birmingham, 1913, p. 496. 



* Giimbel, Die paldolithischen Eruptivgesteine der Fichtelgebirge, 1884, p. 45. 



