VOLCANIC ROCKS OF DARTMOOR. 



291 



In fig. 4 we have a N.W. and S.E. section, passing from Littonary 

 Down on the north to llary Tavy and Ridge on the sonth, and just 

 cutting the southern boundary of Brent Tor. We have here the 

 broadest part of the Heathfield basin. The turn-over of the vol- 

 canic beds c at Monkstone appears to be a probable though by no 

 means a certain rendering. 



Sections 4 and 5 (figs, o & 6) are taken in a l^.W. and S.E. direc- 



is-.w. 



Fig. 5.— Section (4) East of Brent Tor. 



Bowdon. Cross Eoads. 



N.W. 



Fig. 6. — Section (o) Fast of Brent Tor. 



W. Lang- 

 stone. Eoad. 



S.E. 



Eurn. 



tion through the little triangular area on the east of the JBrent-Tor 

 fault. Here the volcanic beds c and d only are represented, and the 

 flexure and northward dip of c must again be taken as an expedient 

 but not very trustworthy version of what may possibly occur along 

 this line. In drawing these sections I have fully accepted the data 

 furnished by the Survey Map ; but, from a short examination of the 

 ground, I am inclined to think that in some few instances the boun- 

 dary lines are not absolutely correct. 



Fig. 7 is a section taken a little west of north through Brent Tor, 

 ranging from Bowdon to Tavistock. Here the whole of the Brent- 

 Tor volcanic series of lavas, agglomerates, tuffs, ashes, and the 

 associated sediments is shown. The fault is also indicated ; and the 

 feeder of the volcano is represented as coincident with the fault. 

 The denuded portions of the cone are also suggested. 



Fig. 8 is a chimoera which maj/ embody a certain amount of truth. 

 Here the downcast is shifted up to its normal position : we see the 

 old furnace in full blast, and its long undisturbed lava-flows a, h, c, 

 and cZ, with tufts, ashes, and sediments interbedded. 



The little black hummock represents what remains of the original 

 cone. 



In fig. 9 I have roughly indicated the possible relation which 

 may exist between the volcanic series of Brent Tor and that of 

 Saltash, the granite of Hingston Down lying about halfway between 

 the two series and pushing up the intervening beds in an anticlinal 

 fold. The dotted lines are mere suggestions of the vast thickness of 

 strata carried from off this area by denudation. I have also indi- 



