ANNTVEESAEY ADDEESS OF THE PEESIDEXT. Ixiii 



one to the other since the mass has occupied its present position. 

 Such a conclusion may still be questioned, even though the change 

 be shown to be a natural one (by the occurrence of a pseudomorphous 

 mineral), and be confirmed as a possibility by the results of laboratory 

 experiment. 



Many of these suggested processes remove us after all by only one 

 stage from the main question of the origin ; for if we concede that 

 the serpentine has been transmuted from a rock of labradorite and 

 diallage (gabbro), or of anorthic felspar and hornblende (diorite), 

 we pass back to compounds which are much more akin to the con- 

 fessedly igneous rocks, and thus find it still more difficult to derive 

 them fi.'om sedimentary strata. 



Our President in 1859, Prof. Phillips, referred in his Address to 

 this vexed question as affecting the great unstratified mass of the 

 Lizard, in Cornwall, and gave us the two opposite hypotheses, show- 

 ing how the occurrence of the diallage rock with serpentine may be 

 made to chime in with both. Eut the argument in favour of the ser- 

 pentine having been originally a stratified mass which has undergone 

 metamorphism is vitiated by the incorrectness of the observations 

 on which it is founded. It is true that on the south of the great 

 body of the serpentine its junction with the hornblendic and mica- 

 ceous slate is obscure ; but on the north there are spots (not 

 unnoticed by De la Beche), as at Pencarrock and Trenithen near 

 St. Keverne, where the slaty strata are decidedly changed by the 

 proximity of the serpentine*, and where they dip off from that rock. 

 Moreover at Kennack Cove, on the south side, may be seen a bold 

 example of the intrusion of a great vertical tongue of this rock, 

 with lateral branches cutting into the black argillaceous slate, 

 Similar, indeed, to the Italian, although on a smaller scale, we have 

 here instances which allow no doubt that the material has been 

 intruded in a plastic state into rocks with which it came into con- 

 tact, leaving it open to us to beheve either in simple fusion, like 

 that of a deep-seated lava, or in that state of plasticity from other 

 chemical action which is offered to us by the Canadian geologists as 

 the more probable condition. 



The gabbro or granitone (Crousa rock) , which forms a fine element 

 in this district, from St. Keveme to Coverack Cove, offers in its 

 occurrence, as it appears to me, no support to the opiaion of its 

 chemical transformation into serpentine. 



Excluding from present consideration a few somewhat far- 

 fetched theories, in which authors have carried to an extreme the 

 liberty of removing by percolating water those elementary sub- 

 stances which are not required and introducing those that are 

 needed for the composition of serpentine, we observe that among 

 those who demur to its igneous origin there are two very opposite 

 views. The majority are satisfied to derive it from another and 



* On my recently showing fragments of nearly adjoining clay-slate to 

 our associate Mx. David Forbes, F.E..S., a thoroughly experienced observer 

 in such matters, he recognized at once the characters of a killas altered by the 

 contact. 



