The N omenclahtre of tlie Keratophyres. 851 



of keratophyres with typical spilites is a proven fact, and that the 

 two are consanguineous can no longer be questioned. If, then, the 

 individuality of the Spilitic Suite be admitted, it becomes necessary 

 to distinguish between Atlantic and Spilitic rocks of like chemical 

 and mineral composition, if such exist. For this reason " soda 

 granite-porphyry " is too wide a term to apply to the intrusive rocks 

 under discussion, as it includes not only these alkaline derivatives of 

 a magma of spilitic afUnities, but also similarly constituted members 

 of what the writer may be forgiven for calling the ordinary Alkali 

 Suite — the Atlantic Suite of Harker. 



It appears, therefore, that there is no name in current petro- 

 graphical nomenclature which has a special claim or, indeed, is 

 specially applicable to these rocks, other than the lava name, which 

 has the further justification of usage in this sense on the Continent 

 for a long period of years. Taking this into consideration, together 

 with the practical identity of mineral composition and micro- 

 structure of both intrusive and extrusive keratophyric rocks, there 

 seems no reasonable objection to iismg the one name for both, there 

 being several precedents for this procedure. The only alternative 

 is to coin a new name for the intrusive equivalents, restricting 

 '■ keratophyre " to lavas. This seems quite unnecessary, and there 

 is much to be said for uniting all these rocks under one name, 

 distinguishing between lavas and intrusions by using the qualifiers 

 " intrusive " and " extrusive ", if this should be thought necessary. 



V. Further Classification of Keratophyres. 



Assuming that " keratophyre " can be so used, it remains to see 

 whether any further classification can be efEected. Obviously such 

 further subdivision cannot be made on the basis of the dark mineral 

 content, as in the great majority of cases no original coloured mineral 

 remains. Some of the Tayvallich keratophyres contain small 

 irregular flakes of either brown or green biotite, but it is doubtful 

 how much of this is primary, some part being certainly secondary, 

 derived from the introduction of basic material from the adjacent 

 pillow lavas. ^ Only rarely have recognizable pseudomorphs 

 been reported from British keratophyres ; those from Skomer Island 

 appear to have contained both rhombic pyroxene and olivine, the 

 albite-trachytes of the Benton Volcanic Series, ^ the extrusive kerato- 

 phyres of the Trefgarn Volcanics,^ and those of Abercastle all contain 

 pseudomorphs after rhombic pyroxene. The keratophyric 

 " andesite " of the Eastern Mendips is yet another example 

 containing beautiful chloritic pseudomorphs after the same mineral. 

 These are exceptions, however, and most keratophyres contain only 

 scales and fibres of chlorite, even these being far from abundant. 

 There is evidently no basis of subdivision here. The only qualitative 



1 " Geology of Knapdale, etc." : Mem.. Geol. Surv., 1911, pp. 92-3. 



2 Geology of the South Wales Coalfield, part xi, Haverfordwest, p. 6. 

 ' Ibid., p. 22. 



