114 PEOCEEDINGS OP THE GEOLOGICAL SOCIETY. 



and about Aclinasheen) occupy this position in the series. The 

 greenish and lead- coloured schists, with quartzites, in Anglesey, 

 the Cornish schists (though perhaps these are rather older), and 

 those of South Devon, present many resemblances to members of 

 the uppermost zone of the metamorphic rocks of the Alps ; and 

 to these I should refer some of the more crystalline Huronians. 

 The remainder of the Huronians and the red felstones of Canada 

 closely resemble the true Pebidians (including the rhyolites of N'orth 

 Wales). 



It has been often urged that these comparisons are idle ; that they 

 must be made with extreme caution no one feels more strongly than 

 myself. I think observers have frequently been much too hasty in 

 inferring similarities and asserting discordances. I should make 

 every group as inclusive as possible, and I shrink, almost nervously, 

 from proposing distinctive names. But what is our position ? We assert 

 without fear of contradiction, that every attempt to show that any 

 of these gneisses and schists are metamorphic strata of Palgeozoic age 

 has broken down on examination. They are always much older than 

 any rock which we can date ; some are indubitably long anterior to 

 the Cambrian epoch. So complete has been the failure of these 

 attempts, that we have a right to demand as unprejudiced judges that 

 all the evidence in their favour should be regarded with suspicion, 

 like that of discredited witnesses. Schists and gneisses may be 

 metamorphosed Palaeozoic shales, but the onus jprohandi, according to 

 all the rules of evidence and of reasoning, now lies upon the person 

 who asserts it, and there is so much against the antecedent probability 

 of such an identification, that it can only be admitted on the very 

 clearest evidence. 



If, then, these schists and gneisses are Archaean or Azoic or Eozoic 

 (I regard the name as a very secondary matter), if they are mostly 

 long anterior to the Cambrian, and if in various regions we observe 

 increased metamorphism in a downward direction, and progressive 

 evidence of some kind of stratification in an upward, together with 

 a stratigraphical succession and lithological correspondences not 

 rare but frequent, it seems to me that, as we can have no other means 

 of comparison or correlation, we may fairly use this as a working 

 hypothesis. It will, at any rate, facilitate our labours, and cannot, 

 I think, do anything but good, if we are careful to remember that 

 it is only an hypothesis, and so apply to it honestly the test of every 

 fact that in the process of our work we can regard as established. 



If these strata are of great antiquity, if they are the record of a 

 very early period in the earth's history in which at first a condition 

 of things wholly different from the present must have prevailed, and 

 if there was a gradual approach to those more in accordance with 

 the present, it is highly probable that similarities of environment, 

 and uniformities of deposits would prevail over areas far larger than 

 is now the case. Chemical action, at a time when the earth's crust and 

 atmosphere were at a higher temperature than in later days, would be 

 more intense than now ; precipitation and sedimentation would 

 differ widely in their results when the solvent agents differed and 



