498 MR. B. HOBSON ON THE BASALTS AND 



mingled with the more common red sandstone, which bears a very 

 great resemblance to a volcanic product." 



The Rev. A. Irving ^ says : — " What I have seen in the field, 

 particularly in the Crediton Yalley, referred to in my 1888 paper 

 (p. 159), points ' to the existence of true volcanic agglomerates 

 forming locally integral portions of the Breccia series.'' Tuff is 

 mentioned by Prof. Bucking, in Mr. IJssher's paper, as occurring 

 at Yeoton, near Crediton. I was unfortunately prevented by the 

 bad weather from properly examining the quarry there. 



5. There is a very close agreement in mineral composition and 

 both macroscopic and microscopic characters between the rocks of 

 all the localities, except Killerton and Long Lane, Loxbear, so that, 

 as many of the rocks are clearly contemporaneous, the probabihtie* 

 are all in favour of the rest being so. 



I therefore feel no doubt of the contemporaneous nature of tho 

 lavas exposed in all the localities visited, without for a moment 

 denying the probability that the necks by which they ascended may 

 be hidden beneath the surface-flows ; indeed, De la Beche ^ figures 

 dykes of ' felspathic trap ' at Cawsand in Plymouth Sound intrusive 

 in Devonian rocks, though the evidence that the trap there is of 

 Permian (or Triassic) age is not quite conclusive, and I agree with 

 the opinion expressed to me personally by Mr. Worth that the^ 

 schistose dyke figured by De la Beche on p. 279 of the Report is 

 most probably of much earlier age than, and quite distinct in 

 character from, the main mass of the Cawsand ' trap.' 



As mentioned by Mr. Yicary, " it is a fact of large generality that 

 the strikes of the two formations [trap and Trias (or Permian)} 

 coincide in direction." Examples of this occur at Silverton, 

 Thorverton, Pocombe, &c. The greatest length of outcrop also- 

 usually coincides with the direction of strike, but this does not seem 

 to me to be any reason for doubting the contemporaneous nature of 

 the ' trap.' It appears to me that whether a rock be sedimentary 

 {e.g. the Millstone Grit 'edges ' of Derbyshire), contemporaneously 

 interbedded igneous rock, or igneous rock intruded along bedding- 

 planes, it will naturally tend to have its greatest length of outcrop 

 in the direction of strike, as soon as it is tilted out of the horizontal 

 and denudation sets in. 



III. Improbability op the Former Existence op these Lavas in 

 THE Area op the Dartmoor Granite. ■ 



Mr. R. IST. Worth, having adopted the theory that the granite of 

 Dartmoor and the elvans in its neighbourhood are the relics of the 

 base of a gigantic volcano, argues ^ in favour of the previous existence 



^ ' Suppl. Note to Paper on the Eed Eocks of the Devon Coast Section 

 (Quart. Journ. Geol. Soc. 1888),' Quart. Journ. Geol. Soc. vol. xlviii. (1892) 

 p. 76. 



2 Report, p. 212 : see also R. N. Worth, Trans. Eoy. Geol. Soc. Cornw. 188&;. 

 p. 228, &c. 



3 Quart. Journ. Geol. Soc. vol. xlvi. (1890) p. 80. 



