A HISTORY OF CORNWALL 



Before describing the various formations which compose the Palaeo- 

 zoic system of Cornwall it will be convenient to give a brief description 

 of the general structural features, which have imposed on them their 

 present aspect. This will be more appropriate at this juncture as the 

 geological phenomena to be described are posterior to the formation of 

 the youngest member of the series ; and the chronological sequence we 

 have adopted in tracing the course of our history from the events of 

 to-day back to the remote past will not be departed from. 



From the description of the more recent deposits which we have 

 already given it will be seen that the submarine platform from which 

 Cornwall stands out has been subjected in the past to repeated oscilla- 

 tions, so that the sea-floor of one epoch has formed the dry land of 

 another, moreover the rocky platform of Cornwall itself constitutes, 

 as regards large areas, ancient sea-floors which have emerged from 

 beneath the waves. By these undulatory movements the adjacent bound- 

 aries of land and sea have ever been shifting their position. When it is 

 considered that the Pliocene shore line has been found at an elevation of 

 420 feet, and that the period which separates us from that landmark, in 

 spite of its longevity, is but a fraction of the profound span which 

 extends back to Palaeozoic times, it will require no strain on the imagi- 

 nation to realize that the sediments accumulated beneath the seas of the 

 more distant epoch form the main ingredients which enter into the 

 composition of the Cornish platform. 



Although these Palaeozoic sediments present but little resemblance 

 to the more recent deposits which rest upon them, and to the detritus 

 now being accumulated on our littoral fringe, they are nevertheless to a 

 great extent their counterparts, laid down in bygone geological periods, 

 and thereafter subjected to a series of vicissitudes that have brought 

 about metamorphic changes in their character. The 'killas' of Corn- 

 wall, in spite of superinduced structures which largely mask its 

 original condition, is seen to contain alternating layers of gravel, sand 

 and mud similar to those which are observed in our recent deposits. 

 Moreover, preserved within the strata are the fossil remains of the marine 

 life that flourished in those ancient seas, but of types essentially different 

 from our modern fauna ; while beds of limestone charged with fossils are 

 the result of organic accumulations in clear water free from the inva- 

 sion of sediment. In other words the rocks which enter so largely 

 into the geological architecture of Cornwall belong to an early chapter 

 in the history of that marine plain or great littoral fringe when its 

 boundaries differed widely from those of to-day. Commingled however 

 with the sediments we find the products of volcanic action in the remains of 

 lava streams and ashes, which having been emitted on the sea-floor have 

 been sealed beneath the overlying accumulation. Under the influence 

 of crustal movements the Palaeozoic deposits with their volcanic beds 

 have gradually subsided, and have been buried beneath a deep pile of 

 overlying strata. So great has been their downward movement that they 

 have been brought within the influence of the great laboratory that lies 



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