﻿176 Beports and Proceedings — 



of Hozemont and Grand-Pre is demonstrated to be a gabbro, but its 

 relation to the other rocks is not known. On the other hand, the 

 quartziferous porphyry of Spa is undoubtedl}' intrusive, and so are 

 the quartzose Diorites of Quenast, Eebecq-Rognon, and Lessines. 



As we have hinted at before, the nomenclatiire of crystalline rocks 

 is becoming a matter of increasing anxiety to the geologist. The 

 present authors are to be complimented on the simplicity of the 

 system they have adopted. One example will suffice : under the 

 term " diorite quartzeuse," they designate a rock on which the 

 following names have at various times been bestowed, viz. : 



Porfliyrite, Zirkel. Porphyritic cliahase, Nauuiann. Quartzose 

 porjjhyry, Delesse. OUgoolase purphyry, Eoth. Chloropli'yre, Dumont. 



Synonymy is an evil which geology will sooner or later have to 

 deal with, both as regards lithological and stratigrapliical nomen- 

 clature, and the sooner some broad rules are accepted by the majority 

 of the leaders of the science, the better. At present, in examining 

 geological maps, or in reading geological works, half our time is 

 wasted in finding out (if we do find out) what is meant by the 

 terms used. Zoologists and Botanists are fortunate in having some 

 generally-recognized laws of priority, tempered to' some extent by 

 fitness, and it certainly does not appear why Geology should con- 

 tinue to lack any relief of a more or less similar character. — G. A. L. 



I2,:ei=o:e^ts -i^i>riD :Fi?,oo:E]:EnDi2src3-s. 



Geological Society of London. — I. — February 7th, 1877. — 

 Prof. P. Martin Duncan, M.B., P.E.S., President, in the Chair.— 

 The following communications were read : — 



1. " On the Chemical and Mineralogical Changes which have 

 taken place in certain Eruptive Eocks of North Wales." By John 

 Arthur Phillips, Esq., F.G.S. 



In this paper the author described the felspathic rock of Pen- 

 raaenmawr, which has been erupted through Silurian strata, and 

 rises to a height of 1553 feet above the level of the sea. The rock, 

 which is composed of crystalline felspar with minute crystals of 

 some hornblendic mineral, is fine-grained and greenish grej^ divided 

 into beds by joints dipping north at an angle of about 45"^, and 

 again divided by double jointings, sometimes so developed as to 

 render the rock distinctly columnar. At the eastern end of the 

 mountain the stone is so close in texture as often almost to resemble 

 chert. In the next two quarries westward the rock is coarser, and 

 its jointing less regular. In the most westerly quarry the stone is 

 generally fresher in appearance, closer in grain, and greener in 

 colour. All these stones are probabl}'^ modifications of the same 

 original rock. From the chemical analysis of the rocks the author 

 concludes that, supposing them all to have had originally the same 

 composition as the unaltered rock in the most westerly quarry, that 

 at the extreme east of the mountain has lost about 3 per cent, of 

 silica, and the others have received respectively an increase of 1'35 



