HOLL — MALTEKN HILLS. 99 



tions of more frequent osciUations of level in Europe than there are 

 in North America ; and whether the rocks which immediately overlie 

 them in any particular district should be Cambrian, or Silurian, or 

 even of more recent age, depended solely upon the relative distribu- 

 tion of land and water at the period of their deposition. The results 

 of later investigations into the physics of the ocean show that the 

 detritus obtained from the wear and tear of dry land, after being 

 carried for a distance out to sea, is washed back again to the con- 

 tinent from whence it came, and that the debris of an oriental con- 

 tinent contributes nothing to the sedimentary deposits of an occi- 

 dental, and vice versa*. Hence there is no reason for expecting to 

 find the Lower Cambrian a more generally or widely spread system 

 than any of those that succeeded to it. 



Although, therefore, there is no direct evidence to enable us to 

 say that these Malvern crystalline rocks are the exact equivalents in 

 time of the similar rocks on the northern side of the River St. Lau- 

 rence, neither can we correlate those of Scandinavia or the Hebrides 

 with them with greater certainty ; but there is, I think, evidence that 

 will enable us to say that they all of them form a part of the great 

 Pre-Cambrian system, which is a "universal formation "f, and of 

 which the Laurentian rocks of Canada are western representatives. 



The grounds for concluding that the Malvern range was sinking 

 during the period of the deposition of the HoUybush Sandstone and 

 Black Shales have been already explained, and it is quite consistent 

 with this view that the period should have been one of active volcanic 

 action ; for it is probable that slow, and perhaps intermittent, subsi- 

 dence may be one cause of volcanic activity t, although the first out- 

 burst is said to have been more commonly attended by elevation §. 

 This activity appears to have been less in the period of the sand- 

 stones than it was in that of the shales ||, but, owing to the overlap, 

 we have no means of knowing what thickness of these sandstones 

 lies deeply below the lowest beds exposed at the present base of the 

 hiUs. 



Even supposing a more extended acquaintance with the fossils 

 of these sandstones and shales should not finally establish their Pri- 

 mordial age, but group them with the Llandeilo series, this would 

 not, it appears to me, in any way affect the probable age of the meta- 

 morphie rocks below. No doubt the occurrence of the entire Cam- 

 brian and Cambro-Silurian series would establish their Azoic age ; 

 but the absence of some of these Palaeozoic beds does not prove them 

 to be the less ancient. These Malvern HiUs may have stood up as 

 an island in the Primordial sea, while, as it subsided, Cambrian and 

 Cambro-Silurian strata were accumulated around it. 



"What higher beds were superimposed upon the Dictyonema-shales 

 we have no means of ascertaining. That the subsidence was arrested 



* Dana, op. cit. p. 659. % Idem, p. 695. 



t Dana, op. cit. p. 135. § Jukes, Manual of Q-eology, p. 344. 



H Since this paper was written, Mr. Salter has called attention to the occur- 

 rence of volcanic ash-beds in the Upper Lingula Flags of St. David's Head. 

 Quart, Journ. Geol. Soc. vol. xx. p. 241. 



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