l-KKMIIiKNT S A()r)KKHH. XIII, 



cryHtfiln, vvlii(-li arc snuiowlifit, oloii^'atcd {iiid yit\\</h\y pfrpcii 

 (licular tf> tlio jimctioii, t'oniiiii^' a HOrt of friii^o. On tlw! oUmr 

 liaiul, a jniictioii of scliiHt and f^'ianito from IJrazil Wood, luiir 

 Lc.ic.o.Hior , shows a inoHt. curiously iiuhd.csrmiiiii.t.fi /oiki, wliicli, 

 althon^'li (licro is a vory inarkfid clian^^(! of colour and t,(!xf,iirc, 

 scemH difficult to assi^Mi definitely to (utlicr tli(! (i.ltci(;d or tlic 

 altoniif< inasM. 



The discussion lias oidy hc<^'iiii, for wc may he siirc' tiifi.l the 

 fliipportors of the liy{)otlicsiH of an Arclifnan syHtcni will not 1)0 

 easily driven from their position, and will require much more 

 definite and nnmistakcahlc evidence of the intrusion of the fjrai I itoid 

 rock than has yet been adduced. The microscopic evidence is not 

 very certain. Unfortunately there seems no certain mr^tiiod at 

 present known of discritninatitif,' between what we may |)(^rlm.|)s l)e 

 allowed to call tniefjranites.and whatare now called ^'ni.nitoidites. 

 Prof. JJonney speaks of " a somethin,^' hard torlescrihe in words 

 tliat differentiated this Crystalline rock of Ht. David's from all 

 tlie undoubted fjranites with which lie was acquainted;" hut 

 acknowledges that tlie decision is most difficult; and that It is 

 HO we may Hee from the fact that, on the one luuifl, such practised 

 observers af^ Prof. Ptcnard, Prof. Zirk(!l, and Prof. Wichmann 

 report " tliat the so-called I)imetian n)ck of St. David's is 

 nnqncstionably a true f,'ranite," while, on tlie other, Mr. Davies 

 did not admit that some of the rocks cited were ^'ranites at all, 

 and said that, arnonf,' five hundrfid specimens from about four 

 hundred localities, he could find nothing rescmblin;^' tlic Ht. 

 David's rock, and added, that in the very heart of this supposed 

 intnisive mass was found a breccia with fi-afjments (some of 

 them water-woni) of the stratified rr)ck of the district. The 

 last sentence of Mr. Davies' remarks introduces fi, furthei- point 

 in dispute. Dr. flicks, and those who a^'re(! with him, tell us 

 that a great part oi the pebbles of the admittedly Cambrian 

 conglomerate is derived from the older volcanic and metamorphic 

 systems. On the otlier hand, the official geologists contend 

 that they are almost all quartz or quart/ite, and that there is 

 no indication of the older rock of which they arc fragments. 



