576 Correspondence — Prof. T. G. Bonnet/. 



of Karak clews, and at Coverack this is the case. Serpentine is a 

 decidedly brittle rock. Any one who knows the Alps is familiar with 

 its pressure-modifications. Yet the serpentine at all these three 

 places, as a rule, is singularly perfect in its structure, free from 

 all indications of serious mechanical disturbance. There are, I am 

 well aware, serpentines at the Lizard which might be quoted as 

 evidencing 'pressure-structure,' but, as it happens, these do not 

 occur at any one of the three localities where the foliated gabbros 

 exist. At all three the serpentines are perfectly normal in their 

 characters. But it might be asserted that, at the epoch of the pressure, 

 the serpentine existed as a peridotite, and this very possibly would 

 be true ; still I think I know what is the effect of pressure on a 

 peridotite, and could conjecture what the results would be when 

 it was converted into a serpentine, and of these also I find no signs 

 at the above-named places. 



But it may be argued that this foliation in the gabbro is the 

 result not so much of a general compression of the district, as of 

 local strains, thrusting, and shearing in the gabbro-mass itself, due 

 to local disturbances ; that it is a structure resulting from faulting 

 rather than from folding — from dislocation-strains rather than com- 

 pression-thrusts. So far as the minor cases at the Balk and Coverack 

 are concerned, this explanation would seem feasible, but it is difficult 

 to apply it to such an enormous mass as that of Karakclews, 

 where the differentiation and parallel ordering of the minerals have an 

 extraordinary development. Moreover, as Mr. Teall justly says, 

 this mass sends out veins into the neighbouring serpentine, and that 

 rock to the north has been repeatedly pierced by small gabbro veins, 

 so that we cannot suppose the main mass to have been thrust far 

 away from its original position. 



There are then, as it seems to me, some serious difficulties in 

 applying the theory of pressure-foliation to the Lizard gabbros, if 

 it be assumed that the structure was produced in a solid rock. Mr. 

 Teall's solution of the difficulty may be the right one, but it is always 

 well to look at all sides of a question. A new answer to one of 

 Nature's greater riddles is often rather a first approximation to the 

 truth, than the actual truth, and stands in need of subsequent 

 modification. As at present advised, I am disposed to think this the 

 case in regard to the Lizard gabbro, though further study may 

 remove my difficulties. Still I think we shall do well to proceed 

 cautiously in regard to this new hypothesis of pressure-metamorphism. 

 It has come to many, like myself, almost as a revelation, pouring 

 a flood of light upon a number of dark enigmas ; but for all that we 

 must not allow it to dazzle our eyes. In this, as in so many other 

 things, reason should go hand in hand with faith. T. G. Bonney. 



Necrology. — We have to record with deep regret the recent losses hy death of 

 Dr H Abich, F.M.G.S. (Vienna); Mr. George Busk, F.R.S., F.G.S. ; Kev. W. 

 Downes, B.A., F.G.S. ; the Earl of Enniskillen, D.C.L., F.E.S., F.G.S. ; Mr. 

 Caleb Evans, F.G.S. ; and Prof. F. Guthrie, F.R.S., F.G.S. 



Erratum.— Geoi. Mag. November Number, p. 492, line 10, delete "difficult." 



