ASSOCIATED EOCKS OF TEH BEEIDDEX HILLS. 543 



is a little still left. That it has once been a glass, I think, admits 

 of little doubt. In some of the specimens were indications of flow- 

 structure ; out of this magma the pyroxenes appear to have crystal- 

 lized first, and then the felspars. The average sp. gr. of the rocks 

 is 2-66. 



This description makes it pretty evident that we have here a group 

 of andesites of that type becoming so widely known now as bearing 

 rhombic pyroxene. This particular group appears to deserve the 

 name of enstatite-andesites, or some might prefer to call them 

 enstatite-porphyrites. Prof. Bonney says, " I could imagine some of 

 the lavas I have from the Andes getting to look like this rock ;" and 

 the resemblance between their structure and that of the Eosenau 

 andesites is most marked. 



Most of them are undoubtedly lava-flows, and have been denuded 

 to form conglomerates, the pebbles of which obviously consist of 

 this rock, and the microscope completely confirms the identification. 

 The ashy matter in which the pebbles are imbedded consists of 

 broken crystals, like those in the andesite ; and the Middletown ash 

 might have been formed from such felspar crystals as occur in it. It 

 is, as I have stated before, highly probable that some few of the 

 bosses of rock may be intrusive. There are one or two small veins 

 of it, too, intruded into the ash of Middletown quarry. 



2. Neiuer Series. 



Belan Bank, two hills IN", and S. of the chapel at Bausley — the latter 

 connected with Brimford Wood by dykes — Eodney's PiUar HiU, the 

 Criggan, Poel Coppice, the Little Garreg near Trewern, a small 

 rock near Cefn, at Buttington, and a small intrusion on Bulthey Hill, 

 are all composed of varieties of intrusive igneous rock. 



Macroscopically, it varies from dark grey rock, in which there are 

 obvious crystals of pyroxene and felspar, to a green type, in which 

 the crystals are less obvious and more decomposed. One rock in 

 Brimford Wood contains a much elongated variety of augite and large 

 felspars, so that it looks at first rather like a gabbro. Amygdaloids 

 occur commonly, particularly at Eodney's Pillar Hill, and there are 

 similar rocks right dovni to the base of the hill, which I examined 

 in the company of Mr. Silvester and some others of my students ; 

 occasionally the vesicular structure is deceptive and due to the sur- 

 face-weathering of some of the minerals ; but in all the massifs some 

 true amygdaloids can be found. The rock usually weathers brown, 

 and is divided into large irregular columns on the summit of Eodney's 

 Pillar Hill. The varieties group themselves under three main heads, 

 so descriptions of specimens from a few typical localities will give 

 the best idea of the structure of the rocks. 



(ci) Eodney's Pillar Hill, Criggan, Belan Bank, and Trewern, 

 This type is green and shows lath-like felspars and pyroxene ; it is 

 granular in aspect, and there is not the obvious ground-mass of the 

 andesites. It is often amygdaloidal, the kernels consisting of calcite. 

 The rock is often ophitic in structure, but frequently there are 

 spaces between the minerals occupied by opacite, apparently an 



Q.J.G.S. No. 164. 2q 



