PKKSIDKNT S ADDKKSS. XI. 



artificially, and we know that some of the compounds of 

 chlorine were present, while the frequent presence of tour- 

 maline and minerals containing lluorine in the contact zone 

 round granite masses is also suggestive in this light. 



^Vhile the conclusions of the Government Geological Survey 

 have thus been hupugned in Scotland, and, as above stated, 

 observers have relegated what were considered to be metamor- 

 phosed Silurian to the Pre-Cambrian, or, as it is now usually 

 called, the Arclnean system, the present Director- General of the 

 Survey, Dr. Archibald Geikie, has made a counter-attack in 

 another district. Some years ago Dr. Hicks announced that he 

 had made observations which went to show that the granitoid 

 rock in the neighbjurhoad of St. David's, in Pembrokeshire, is 

 really a higlily metamorphosed sedimentary mass, still showing 

 obscure bedding planes, and including in the coarse-grained 

 gueissic rock bauds of impure limestone, schists, and dolerites. 

 Succeeding this is a great mass of volcanic rocks, felsites, 

 breccias, and tuffs ; and this again is followed by some com- 

 paratively unaltered slaty rocks. Over all these come tiie 

 Cambrian strata, recognisable by the fossils, which Dr. Hicks 

 himself has done so much to bring to light. The three great 

 formations first mentioned are, therefore, Pre-Cambrian or 

 Arcliffiau. A similar succession has been observed in several 

 other parts of our island ; crystalline gneisses or granitoid 

 rocks, schists, quartz-felsites, and volcanic tuffs, making up 

 such regions as that constituting the Wrekin area, Malvern, 

 parts of North Wales, and Anglesea. In fact, the St. David's 

 district has seemed to give the key to the structure of most of 

 the Archaean tracts of Britain. Although the exact correlation 

 of the formations is still undecided, it may be mentioned that 

 the researches of Prof. Lapworth and Mr. W. J. Harrison have 

 brought to light in oiir immediate neighbourhood, at Nuneaton, 

 quartz-felsites, and ash-beds, underlying, and apparently 

 supplying, the material for the quartzite which, it seems prob- 

 able, is, ni its turn, succeeded by shales containing Cambrian 

 fossils. In Leicestershire again there is a certainly very ancient. 



