ON tilE AllCII.KAN EOCKS OF (JRKAT LRITAIN. 



531 



laceous 



, of the 

 .tratifiecl 

 turesque 

 A of the 

 ;cction is 

 n of the 

 vmoi'pliic 

 ich, liow- 

 arcation 

 1, as eacli 

 sties, it is 



uitrusion 

 ; probably 

 ,s of sharp 

 n districts 



follow the 

 tie geology. 



dull green 

 ily decided 

 e, are ('om- 

 imes -sN'ith :> 

 igated on a 

 ire in mwr^)' 

 completely 

 ion, are seen 

 le, of a ti'i'cei' 

 of a little 

 arnet (rare). 

 jeen nuneval*- 

 it the namf 

 Beche,' ^^> 

 [ere does not 

 ned. occurs ft 

 ,orc coarsely 

 o-rccn micas 

 li^e (V), v'itb 

 ,,.cll exposed 

 novthoftk 

 . Its strise 

 erly side bat 

 I exposed lOf 

 dhv Cove.'- 

 :tensively de- 

 and western 

 srticftl thick- 



L intevbeddeJ. 



ness of it must be exposed. It is a distinctly bedded, strong, hard rock, 



oidy slightly fissile ; sometimes quite massive in fracture, and almost like a 



diorite, but in other places exhibiting very distinct alternating laminations 



differing in mineral character. The materials are distinctly crystallised, 



though they do not generally exhibit a definite crystalline outline. The 



dominant mineral is hornblende, macroscopically a dark green, almost 



black, microscopically a rich green, strongly dichroic. With it occur in 



variable quantities the following minerals : quartz, felspar (generally, so 



far as is recognisable, a plagioclastic variety), and epidote, with more or 



less magnetite, pyrite, &c. ; occasionally the felbpur occurs in rather irre- 



o;ukr ' eyes,' giving a subporphyritic chai'acter to the rock, but as a rule its 



texture does not very greatly vary. Occasionally the absence of any 



distinct structure makes the rock almost indistinguishable from a diorite 



of moderately tine texture ; but often it is beautifully banded, layers of the 



qnartzose, fcispathic, or epidotio constituents alternating with those in 



which hornblende predominates. The bands miiy vary in thickness from 



half an inch or more to mere films. They are parallel with the apparent 



rather ' slabby ' bedding which is generally characteristic of the series. 



Farther, at a place called Hot Point, is a structure which, although the 



rock is perfectly crystalline, is so marvellous an imitation of false bedding 



that it is difficult to believe it due to any other cause than the deposition 



of the original constituents ; these, and indeed much of the grouj), may 



possibly have once been basic tufi's. 



((') GrtninJitic Cwvp. — Into this the one last described passes 

 almost insensibly. It is e\ en more conspicuously bedded than the last, 

 and it is distinguished from it by the prevalence of bands of a lighter 

 colour. The latter consist chiefly of quartz and felspar, with a little 

 hornblende or, less commonly, black mica. Sometimes a specimen resem- 

 bles macroscopically a piece of vein-granite, consisting of little else than 

 quartz and felspar : sometimes it might almost be a fragment from the group 

 above described ; but, as a rule, the hornblende is much less abundant and 

 less definitely crystalline. Thus, macroscopically and microscopicall}', the 

 group is rather readily distinguishable, and, notwithsto ading the rarity 

 and inconspicuousness of garnets, I have ventured to call it the G ranulitic 

 group. It seems impossible to explain the frequent and repeated in- 

 terchanges of lamina^ and bands of these two principal varieties of rock — 

 distinguished so readily by the eye, as the one is a warm, light reddish 

 grey, the other quite a dark gi'oy -except on the hypothesis that they indi- 

 cate original sedimentation, aiid I have described and figured a case from 

 Kennack Cove which seems indicative of irregular lamination.' Owing 

 to the frequent interruption of igneous rocks, and the numerous faults (in 

 which however the throw is probably not great), it is very difficult to assign 

 a thickness to the motamorphic series of the Lizard. The base of the 

 micaceous group is not seen, the hornblendic group must be of considerable 

 thickness, but I should not allot more than tliree or four hundred feet to 

 the granulitic group. 



Ljneoiis lioclcs. — In the above metamorphic sedimentary series we find 

 the following rocks, which it may be well to enumerate, though it is no part 

 of my present plan to describe them in detail. Some of these also are 

 now entitled to the term ' metamorphic,' as they l";ve undergone great 

 mineral changes. 



(a) Serpentine : a very handsome rock ; sometimes almost black, 

 I Q. J. Q. S., vol. x.xxix. pi. 1. 



M M 2 



a 





U 



