The Nomenclature of the Keratophyres. 349 



a terra, and one needijig restriction/ the second that the definition 

 should be widened to ijiclude all intermediate albite-rich rocks, 

 irrespective of their mode of occurrence.^ 



III. Intrusive Keratophyric Rocks. 



With regard to the latter point, the utilization of one name for 

 both lava and hypabyssal equivalent is not without precedent. 

 Indeed, the tendency is growing to place micro-structure before mode 

 of occurrcuce as the diagnostic feature determining the nomen- 

 clature of the rock. Thus " dolerite " and " basalt " are frequently 

 used in a sense which ignores the mode of occurrence of the rock. 

 When such is the case is it not desirable to prefix the rock name with 

 " extrusive " or " intrusive ", as the case may be ? It seems to the 

 writer that a greater degree of accuracy is to be attained by using the 

 lava name for extrusive rocks only, and introducing compound 

 terms where necessary for specimens having textures other than 

 normal. Thus '" doleritic basalt " would signify an extrusive rock 

 with the mineral composition and field characters of basalt, but the 

 texture of dolerite. With the rocks under consideration the case is 

 not so simple, as no distinctive name exists for intrusive keratophyric 

 rocks, other than the lava name. 



Those workers who prefer to restrict " keratophyre " to lavas only, 

 have made use of various names for the corresponding intrusive 

 rocks, among them being " albite-porphyry ", introduced in 1884 

 by Heddle for a porphyritic rock of unique composition composed 

 only of albite, and occurring on Beinn Bri^ghaid, in Sutherlandshire.^ 



Again, " soda-granite-porphyry " has been utilized by the officers 

 of the Survey on at least two occasions ; for a porphyritic rock 

 intrusive into pillow lavas (spilites) at Porthallow Cove in the 

 Lizard District,^ and for a more acid, but closely similar rock, 

 also intrusive into pillow lavas at Tayvallich.^ Synonynious ^\dth 

 the above name is " quartz-albite porphyry ", used for the columnar 

 intrusive felsite of Ynys Bery near the Pembrokeshire coast. "^ In 

 addition to these self-explanatory terms, place-names have 

 occasionally been coined for the designation of intrusive keratophyric 

 rocks ; thus, hirnantite,^ the even less euphonious beschtauite, 

 is briefly disraiesed by Holmes in his recent work, the Nornenclature 

 of Peirologij, as a " soda rich variety of quartz porphyry (= quartz- 

 keratophyre) ". 



Before considering an alternative suggestion, the possibility of 

 using the name " lime-bostonite " (maeuuite) for these rocks claims 



^ Thomas, Quart. Journ. Geol. Soc, vol. Ixvii, 1911, p. 214. 

 ^ Cox, Eep. Brit. Assoc. Birmingham, 1913, p. 496 ; also Quart. Journ. 

 Geol. Soc, vol. Ixii, 1915, p. 316. 



3 Heddle, 3Iin. Mag., 1884, p. 141. 



* " Geology of the Lizard and Meneage " : Mem. Geol. Surv., 1912, p. 186. 



* " Geology of Knapdale, etc. " : Mem. Geol. Surv., 1911, pp. 93 and 94. 

 " Geology of the South Wales Coalfield, part ii, Milford, p. 41 



^ Proc. Liverpool Geol. Soc, 1915, p. 79. 



