VOLCAiaC ROCKS OF KARTMOOR. 287 



or belts which, for the most part, trend in an approximately east and 

 west direction, while on the Avest of Brent Tor they are shown on the 

 Survey map to sweep round in a rude semicircle. These strips, which 

 I shall call the volcanic series, dip at very low angles or are in some 

 places approximately horizontal ; and I believe that in many cases 

 they are repetitions of the same bed or set of beds — a view ably ad- 

 vocated by Dr. Harvey B. HoU in his paper on the older rocks of 

 South Devon and East Cornwall*. 



If this be really so, how can we have one part of a bed situated in 

 the Devonian, and another part of the same bed cropping out in 

 Carboniferous rocks ? yet, as the Survey map now stands, this appears 

 to be the case. Justice must, however, be done to the statements 

 published by Sir Henry De la Beche, since in his Eeport already 

 cited, at page 116, he says " The boundary is certainly unsatis- 

 factory between the Tamar and the granite near Tavistock." Again 

 an important statement occurs at pages 119, 120 : — " In the country 

 near Dunterton, Milton Abbot, Lamerton, Brentor, Mary Tavy, 

 Peter Tclyj, and Tavistock, the mass of schistose ash accompanied 

 by greenstone and other trappean rocks is very considerable. In 

 this district also the geological date of the solid trappean rocks 

 may be questioned ; but that of the schistose ash is clearly the same 

 with the various grits and shales, it being merely doubtful to which 

 of the two great systems of rocks some of the beds may be referred 

 near Milton Abbot, Lamerton, and Tavistock. Some perfectly 

 similar rocks occur in both ; and the boundary between them, as has 

 been above noticed is not clearly defined." 



Further on, on the same page. Sir Henry says, " There can be 

 little doubt that the principal band [i. e. the Milton-Abbot and Dun- 

 terton band of the volcanic series] is included in the upper series, 

 as it can be seen to rest upon very characteristic rocks of that series. 

 With a more southern band of a similar ash commencing with 

 Endsleigh, and which is well exhibited in some quarries on the line 

 near Combe, continuing thence by Lamerton and Kilworthy to 

 Sowtentown, there is not the same certainty.'^ With the most pro- 

 found respect for Sir Henry De la Beche's opinions, I cannot refrain 

 from pointing out the probability of beds near the junction of two 

 perfectly conformable formations exhibiting alternations in litho- 

 logical character which render it impossible in a very hmited area 

 such as this to speak with any certainty as to the precise formation ; 

 and since Sir Henry adduces no palseontological evidence in support 

 of his opinion, I think it becomes an open question whether weight 

 should or should not be attached to his statement. The point I wish 

 to establish is this, that we have at Saltash, as recorded by Mr. J. A. 

 Phillips, some schistose lavas in the Devonian series identical with 

 some of those which occur in the Devonian series further north, in the 

 neighbourhood of Tavistock — and that similar rocks occur still further 

 north, round about Brent Tor, and trending westward as though 

 they belonged to the Launceston and St.-Clether series of erup- 

 tive rocks which are included in the Devonian area. If, then, the 

 * Quart. Jouni. Geol. Soc. 1868, vol. xxiv. p. 407. 



