80 ME. E. ISr. WOETH ON THE IGNEOUS CONSTITUENTS OE THE 



and stratigraphical relations of these traps remains to be considered. 

 They are traversed at so many points by felsitic dykes that this 

 association has a constant and not a merely casual character. Mr. 

 Yicary noticed these dykes and their strong resemblance to elvan 

 courses, though, as " a matter of convenience," calling them 

 sandstone*. Mr. Etheridge, P.E..S., suggested that a " dike-like 

 line " in an example submitted to him by Mr. Vicary from Posbury, 

 " appeared to be an elvan." 



Sir H. de la Beche remarked, " the quartziferous porphyry near 

 Dunchideock closely resembles some elvans in all except colour " t, 

 an exception which my experience shows does not hold good. 

 Mr. TownshendM. Hall, E.G.S., in 1879 J announced the discovery of 

 a granitoid vein traversing the Triassic outlier at Portledge, which 

 " appeared to be a true porphyritic granite." I have myself found 

 within the past few months fragments of syenitic veinstone closely 

 associated with the Cawsand trap. 



When we add to this the occurrence of veins of porphyritic 

 felsite traversing fragments of felspathic trap in the breccias and 

 conglomerates, the chain of evidence seems complete that these 

 felspathic traps are comprised within the period of igneous activity 

 represented by the Dartmoor elvans, and that therefore Sir H. de la 

 Beche was right in suggesting a connexion between the two, though 

 this connexion was probably much more intimate than he suspected. 



It is perfectly clear that there are no rocks to be seen now in 

 situ which can have yielded the examples of felspathic trap found 

 in the conglomerates in the neighbourhood of Dawlish and Teign- 

 mouth and thence to the southward ; for these fragments must have 

 come with their granitoid and schorlaceous associates from the 

 direction of Dartmoor ; and not only are there no exposures of such 

 rocks between the conglomerates of this district and the Moor, but 

 no places where they could be hidden from view unless it were by 

 the deposits of the Bovey basin, which for other reasons may be 

 dismissed. Lava-flows, it is true, might be wholly removed and 

 leave no trace in place behind ; but necks and dykes cannot be got 

 rid of by denudation in any such way, and would still be apparent. 



The fact that these fragments came from the direction of Dart- 

 moor, coupled with the absence of any locality between Teignmouth 

 and Dawlish and their vicinities and Dartmoor whence they can 

 have come, thus points directly to Dartmoor itself as their source. 

 If that great granitic plateau is the base of a volcano, and if the 

 granites now exposed passed upwards into felsites, rhyolites, and 

 volcanic rocks, all is perfectly clear ; but I cannot see that any other 

 hypothesis will meet the case. 



The great bulk of the igneous fragments of these breccias and 

 conglomerates is more or less of a volcanic type, and the Plutonic 

 examples, though present, are comparatively few. The former 

 represent an enormous amount of degradation and denudation, which 



* Op. cit. p. 47. This character is often simulated by elvaus. 



t Report, p. 217. 



+ Trans. Dev. Assoc, xi. pp. 430,431. 



