Vol. 52.] ROOKS OF THE LIZARD DISTRICT. 37 



condition, as we approach the other edge of the slice, we pass back, 

 speaking in general terms, through the conditions already described. 



I have again examined the sections at Henscath, Carnbarrow, and 

 in Porthallow Cove. As regards the first and second, I could fill a page 

 with minute descriptions, but may content myself with saying that 

 I found it impossible to explain what I saw, either by displacements 

 due to earth-movements, or by the flowing together of differentiated 

 magmas, or by anything else than the intrusive action of the 

 serpentine on the hornblende-schist, after the latter had become 

 solid. As for the Porthallow sections, it may suffice (except in 

 regard to one interesting detail) to refer to what has been already 

 published, and to copy the words which I wrote on the last occasion 

 in my journal : — " Some of the cases here are inexplicable to me on 

 any hypothesis other than that of an intrusion of the serpentine into 

 the schist. It may be said that ' the two have flowed together/ but 

 the serpentine sometimes cuts across the edges of bands in the other 

 rock in a way which suggests direct fracture and not the result of a 

 strain-slip. The serpentine may indeed sometimes bend with the 

 bands, but that proves no more than that the schist (like the included 

 fragments of gabbro near Manacle Point) has been somewhat softened 

 and made flexible. The bending cannot be attributed to subsequent 

 earth-movements, because the serpentine does not show the slightest 

 sign of crushing, and the weld between the two rocks is often perfect" 



But an examination of the specimens collected on this occasion has 

 enabled me, as the result of the whole work, to clear up a difficulty 

 which this Porthallow serpentine hitherto had presented. We find 

 here and therein it, close to junctions with the hornblende-schi&t, grey 

 bands, which are intermediate in aspect and hardness. Is this a less 

 pure variety of serpentine, a streak of picrite, which, as indicated by 

 the analysis, is present in the rock ? and, if so, how can we explain 

 its presence ? 1 I had hitherto vaguely referred it to some 

 differentiation in the magma, but can now offer a more precise 

 explanation, in accordance with the cases already described. I 

 brought away a few specimens for further investigation. One of 

 these, about 4j inches long, consists mostly of the ordinary 

 Porthallow serpentine (a little redder in colour than usual) ; the 

 remainder, a band about an inch thick, is of a greenish-grey colour, 

 and this was in contact with, though here not welded to, a dark- 

 grey, minutely speckled rock, which in hardness and general aspect 

 agreed with a hornblende-schist. The latter, on examination with 

 the microscope, exhibits traces of a banded structure; in some 

 bands are residual grains of felspar, and with them grains of brown 

 hornblende, but the greater part of the rock consists of flakes or 

 longish prisms of actinolite in a felted mass of the same or of a 

 colourless chlorite. The red part of the other specimen is a fairly 

 normal serpentine (Porthallow type). It consists chiefly of the 

 peculiar orange-coloured granular serpentine (mineral), often much 

 stained with haematite, the latter also occurring in minute rods, 



1 See paper by Gen. M c Mahon and myself, op. cit. pp. 471-475, and table 

 of analyses (facing p. 466). 



