18 



THE GEOLOGIST. 



here and there at very long intervals. I will not undertake to say 

 that it contains no limestone detritus, but I certainly have never 

 seen or heard of a fragment of the kind, though I have frequently, 

 and with considerable care, examined the gravel, and questioned the 

 men who work amongst it ; yet the limestone is one of the oldest 

 rocks of the district. Accepting this negative evidence as trust- 

 worthy, it simply proves that the direction of transportation was not 

 from the south ; not that the rOcks in that direction have been called 

 into existence since Bovey Plain received its surface covering. 



But to return. The facts now in our possession appear to compel 

 the belief that the Dartmoor granites were not in existence when the 

 carboniferous rocks of Central and North Devon were deposited, but 

 did exist and were exposed at the surface in the red conglomerate era. 

 In relation, then, to the stratified rocks of the county, we have both 

 an ancient and a modern chronological limit for the granites. Our 

 next question is, What are the places of the limiting rocks in the 

 chronological series of the geologist ? 



There is no difficulty as to the answer respecting the ancient limit 

 — the carboniferous beds. Professor Sedgwick and Sir E. I. Mur- 

 chison, in their paper already quoted, say "the flora of the upper 

 culms, as far as it has been ascertained, agrees specifically with the 

 known flora of the Carboniferous period.. W e think we have strong 

 direct evidence to establish our position that the upper culm strata 

 of Devon are the geological equivalents of the ordinary British coal- 

 fields. "* The same authors, in a passage previously quoted, state 

 that " the upper division of the culm series contains fossils identical 

 with those in the upper division of the coal-measures." 



It is not so easy to settle the modern limit — the red sandstones 

 and conglomerates. That they belong somewhere between the Car- 

 boniferous and Jurassic systems there can be no doubt, since they 

 overlie the culmiferous beds and pass under the Lias ; but whether 

 they are Triassic or Permian has not been considered so certain as 

 could be desired. They are entirely destitute of fossils, excepting 

 those only which occur in the calcareous pebbles, which, of course, 

 belong to the age of the parent limestone. The sandstones are evi- 

 dently of littoral origin ; their surfaces frequently display ztvrre-ripple 

 marks, desiccation cracks, and impressions of rain-drops ; but no foot- 

 prints or other organic traces have ever been detected on them ; 

 they apparently contain no palseontological evidence whatever of 

 their age. 



More than one eminent geologist has been struck with the angular 

 character of the fragments composing the so-called conglomerate, 

 — more correctly, breccia, — and has remarked that in its physical 

 character and general appearance the formation is rather Permian 

 than Triassic. It is, however, as is well known, coloured on our 

 geological maps as being on the horizon of the lower Trias. I am 

 not without hopes than the granite pebbles so frequently mentioned 

 here may help to show that this decision is correct. 



* Geol. Trans., 2nd series, vol. v. part iii. p. 682. 



