Vol. 57.] AMOIJ-G THE MALVERN CAMBRIANS. 179 



Under these circumstances it seems permissible to suggest that we 

 are dealing with an assemblage of rocks which have had a common 

 origin. The most striking difference between the two districts 

 consists in the greater abundance of hornblende in the J^T uneaten 

 area, and of augite in the Malvern district. In addition, a por- 

 phyritic character and flow-structure seem to be much more 

 pronounced in the Malvern rocks. These three features give to the 

 latter a more basaltic or andesitic habit. Some of the differences may 

 be due to differences in chemical composition, but it seems possible 

 that the Nuneaton rocks may have consolidated at a somewhat greater 

 depth than did those of the Malvern area, and that the material 

 which in the former crystallized out largely as hornblende, in the 

 latter mostly took the form of augite. This hypothesis may, per- 

 haps, account for the sharper separation of the different Malvern 

 types ; for differentiation may be supposed to have progressed with 

 increasing distance from the more deeply-seated source. 



According to this view the rocks may be contrasted as follows : — 



Nuneaton. Malvern. 



1. Amphibole-camptonites devoid of 1. Ampbibole-camptonites and augite- 



oliviae and augite. basalt, both of andesitic habit, 



devoid of oUvine, but with augite 

 in the groundmass. 



2. Olivine-camptonites with amphi- 2. Olivine - basalts, often andesitic, 



bole-needles. with augite - microlitea in the 



groundmass. 



3. Ophitic olivine - amphibole - dia - 3. Ophitic oli vine-diabases. 



bases. 



It should be observed that in some of the Nuneaton camptonites 

 and diabases, augite is an important constituent ; such rocks serve 

 to connect the two districts. 



Hocks of the Nuneaton type are not limited to the two districts 

 compared. Prof. Watts records allied rocks in Shropshire,^ and it 

 is probable that certain rocks occurring in the Scottish Highlands, 

 Anglesey, North Wales, and Charnwood, belong to the same 

 category.^ 



IX. SuprosED Pyroclastic Eocks. 



Allusion has already been made to the fact that Murchison and 

 Symonds regarded the Hollybush Sandstone as a volcanic grit 

 (pp. 156 & 157). Phillips did not accept this view,-"^ and I shall 

 endeavour to show in a later communication that the Sandstone has 

 not the least claim to this title and furnishes no evidence of contem- 

 poraneous volcanic action. Timins in 1867 analysed ' some thin 

 beds, apparently formed by the deposition of felspathic ash.'^ He 



^ Proc. Geol. Assoc, vol. xiii (1894) p. 336, & Quart. Journ. Geol. Soc. 

 vol. Iv (1899) p. 1G9. 



^ J. J. H. Teall, Geol. Mag. 1886, pp. 851 et scqq. 



° ' Geology of Oxford & the Valley of the Thames ' 1871, p. 66. 



3 



* Quart. Journ. Geol. Soc. vol. xxiii (1867) p. 356. 



