Vol. 52.] ROCKS OF THE LIZARD DISTRICT. 41 



genesis of the 'granulitic group ' and the hornblende-schists, I adhere 

 (except in regard to a few matters of detail) to the conclusions 

 which were expressed in my paper published in 1877, and more 

 emphatically than ever to those expressed in the first three of the 

 above paragraphs — namely, that I can find no ground for attributing* 

 the foliated or banded structures, whether in the granulitic and the 

 hornblendic groups or in the serpentine, gabbro, and a few basic 

 dykes, to dynamo-metamorphism. As regards the banding of the 

 granulitic and hornblendic rocks, I can only say that if it be due to 

 any kind of shearing in solid heterogeneous materials — it is not easy 

 to follow mentally the steps of the process — recrystallization has been 

 so complete that the usual indications of such action have vanished. 

 Hence the structure must have been produced anterior to the incoming 

 of the serpentine and the gabbro. Yet, if the serpentine were folded 

 together with the granulitic rock so as to distort its bands, traces of 

 crushing and shearing should be found in the latter. Even if we 

 assume these to have disappeared (which I could not admit) and 

 claim the foliated and banded structure occasionally exhibited by the 

 gabbro as a result of dynamo-metamorphism, what is the testimony 

 of the serpentine ? It is sometimes welded to the granulite, often 

 to the hornblende-schist ; it is constantly cut intrusively (every- 

 body, I believe, grants this) by dykes or veins of gabbro. But the 

 serpentine almost invariably shows no signs of crushing. Strain and 

 pressure might destroy a weld, but I never knew them produce one 

 between rocks of this kind ; hence the foliation and banding of the 

 serpentine cannot be due to any such cause. 1 



But serpentine is a much more brittle rock than granite, horn- 

 blende-schist, or gabbro; the last, as one quickly learns in the 

 Alps, being a very obdurate material. Hence earth-movements, which 

 would affect these rocks, would leave their marks distinctly enough 

 on the serpentine. This is a brief summary of my observations in 

 regard to it. Under strain, perhaps under moderate pressure, serpen- 

 tine simply brecciates 2 ; when the pressure becomes more severe 

 the rock breaks into pieces, which are generally rather lenticular 

 in shape, with a ' glaze 'on the outside, 3 and, as a final stage of the 

 4 peine forte et dure,' the serpentine becomes so slaty that it might 

 be sometimes used for roofing purposes. 4 The Alps afford many 



1 On this point I am not afraid of being accused of speaking dogmatically. 

 My first visit to the Lizard was in the autumn of 1873, and I speedily fell a 

 victim to the fascinations of serpentine, probably because I found it to be a 

 subject where quot homines tot sententice held good. I have never felt strongly 

 attracted to beaten paths. Since then I have studied serpentine (including 

 peridotite) in the field on an average once in a year. I have returned five times 

 to the Lizard, I have been thrice to Anglesey, I have examined the rock in 

 three districts in Scotland, in at least a dozen separate localities in the Alps (in 

 some cases not only as a passing traveller), in two districts of the Apennines, 

 and in the Pyrenees, besides studying with the microscope specimens collected 

 expressly by myself, with many others acquired by gift or by purchase. The 

 effects of earth-movements also are not novel to me, since for more than a 

 dozen years I have been studying these in the Alps and elsewhere. 



2 Geol. Mag. 1879, p. 365. 



3 Ibid. 1880, p. 538, and elsewhere. 4 Ibid. 1890, p. 533. 



