Frof. T. G. Bonney — Remarks on Serpentine. 407 



former case, it designates a group, rather than a single species, 

 including a number of forms (generally rather minute), which physi- 

 cally, and perhaps chemically, differ considerably, and agree only in 

 having a hydrous silicate of magnesia as a dominant constituent. 

 Starting, then, from a confusion, probably inevitable, the matter is 

 made infinitely worse when we come to the rock. The name has 

 been applied to all kinds of more or less unctuous, rather dark- 

 coloured (especially green) rocks with a rather even compact ground- 

 mass : in fact, it has been applied, to my knowledge, to rocks which 

 have so little chemical or physical resemblance as to have no more 

 claim to be united under one name than compact basalt and black 

 argillite, or mica-trap and mica-schist. Whatever, then, I assert or 

 deny about a serpentine in this paper must be understood as 

 referring to a restricted group of rocks of which the well-known 

 serpentine of the Lizard in Cornwall, of Portsoy in Ayrshire, of 

 Monte Ferrate in Tuscany, to take one or two cases, are excellent 

 examples. This group is as well defined and limited, when in its 

 normal condition, as any basalt or diorite. In the field, in the hand 

 specimen, under the microscope, it has well-marked characteristics. 

 In its behaviour as regards jointing, weathering, etc., in its accessory 

 minerals, in its analyses, it varies no more than an andesite or a 

 phonolite, or any other species of igneous rock. That intermediate 

 forms may be found linking it on to other species of igneous rock is 

 no more than can be asserted as an objection to every definition of a 

 rock species, so far as my knowledge goes. Thus, by the word ser- 

 pentine, applied to a rock, I mean such a one as that which occurs 

 at the Lizard, for a full description of which, in order to save 

 valuable space, I may refer the reader to my papers on that and 

 other districts.^ 



But before proceeding to discuss Dr. Sterry Hunt's objections to 

 my view that such serpentine is a rock which was of igneous origin, 

 and has been produced by the hydration of a peridotite, I must call 

 attention to some inaccuracies in his references to my work. This 

 is not done merely for the purpose of cavilling, but because, in 

 reading those parts of his paper which refer to myself, I notice a 

 general unprecision of statement, of which these are instances more 

 readily appreciated. This causes me to receive with considerable 

 doubt statements relating to matters beyond my personal know- 

 ledge, because I have noticed as a matter of experience that in- 

 accuracy in recording the meaning of authors is not unfrequently 

 associated with inaccuracy in observing the facts of nature. After 

 stating rightly that I divide the metamorphic sedimentary rocks of 

 the Lizard District (in ascending order) into a group of ' greenish 

 micaceous and hornblendic schists, a black hornblendic group, and 

 a group with granitic bands,' to which (for want of a better name) 

 I gave that of the ' granulitic ' group. Dr. Sterry Hunt proceeds 

 (p. 178) : "It is in the lowest of these three divisions, consisting 



1 Quart. Journ. Geol. Soc. vol. xxxiii. p. 884 ; vol. sxxix. p. 1. See also vol. 

 xxxiv. p. 770; vol. xxxvii. p. 40. Geol. Mag. Dec. II. Vol. VI. p. 362; Vol. 

 VII. p. 538. 



