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