ANNIVEKSARY ADDEESS OF THE PRESIDENT. 87 



strata mentioned above, the evidence for the Archaean age of the 

 former at present before us is not so strong as in the Lizard district. 



North Wales. 



It is, I think I may assume, needless to occupy your time with 

 proving that the devitrified rhyolites in the Bangor-Caernarvon district 

 are not Lower Cambrian rocks metamorphosed in situ. That hypothesis 

 may be regarded now as having no more ground than the Ptolemaic 

 system in Astronomy. If the microscope is not useless in Geology, 

 we may take it as proved that below a certain well-marked conglo- 

 merate forming the base of the Cambrian there come slaty rocks, 

 grits, and conglomerates or agglomerates of volcanic materials, the 

 exact thickness and the details of this second series being immaterial 

 for my main purpose. Further, it will be now generally admitted 

 that a conglomerate representing either the first-named or one of 

 the latter (which it now matters not) rests in some places on a coarse 

 granitoid rock and is almost wholly made up of its materials. There 

 is also considerable (to my mind convincing) evidence that the rhyo- 

 lites are much newer than the granitoid rock. Hence whatever be 

 the genetic origin of the last, whether it be a true gneiss or whether 

 its gneissoid character (for it is no normal granite) be due to subse- 

 quent pressure, it is vastly older than the Cambrian, and therefore 

 represents some 2)ortion of the Archaean series. If we may venture 

 to argue from lithological similarity, this should represent the gneissic 

 series of Tycroes in Anglesey, which is certainly older than the great 

 mass of the schists of that island ; and these, as I have said, are 

 much anterior to the rhyolitic conglomerate, which cannot be newer 

 than the basement-bed of the Cambrian. 



The stratigraphy of the island of Anglesey is at present in such 

 confusion, and my own work among it has been of so fragmentary a 

 character, that, in accordance with my present plan, I shall pass 

 very briefly over the evidence which it affords bearing on the question 

 of the relation of foliation to stratification and cleavage. But, after 

 the papers of Dr. Hicks and Dr. Callaway, we may, I think, 

 safely admit that the gneisses and crystalline schists of that island 

 are much older than even the earliest part of the Cambrian period as 

 usually defined. What I have myself seen leads me to regard the 

 coarse granitoid gneisses (and I think this wiU generally be admitted), 

 such as those exposed near Tycroes and Llanfaelog, as the most 

 ancient rocks ; these, if we can trust lithological similarity, should be 

 correlated with the older part of the Hebridean series of Scotland. 

 The very abundant, fine-grained, rather fissile, micaceous and chloritic 

 schists I regard as later in age, but still as much older than the 

 Cambrian. There is no valid reason that I can discover for correlat- 

 ing these with the typical Pebidian group of St. Davids, or with the 

 group on the opposite mainland which underlies the basement con- 

 glomerate of the Cambrian series. If there is anything in comparative 

 lithology, the last two are decidedly younger than the schists, and are 

 ])robably the equivalents of the hypometamori>hic series in Anglesey 

 described by Dr. Callaway. These schists, have ndubitably been much 



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