CHAP. XXXII 
DEVONSHIRE 
99 
pact, but contains vesicles and irregular steam-holes. On the east side it 
passes upward and laterally into a coarse agglomerate of its own fragments, 
and in its mass it encloses similar agglomerate. No sharp passage can be 
traced between the two rocks. So far as I could judge, it seemed to me 
that the lava had broken up as it moved along, pos- 
sibly shattered by coming in contact with water. The 
agglomerate is overlain by some reddish ashy sand- 
stone, which fills up the interstices between the slags, 
and is immediately covered by a bed of lilac andesite, 
marking another distinct outflow. 
As in Ayrshire, the lavas of Devonshire are not 
accompanied by any thick accumulation of tuff. The 
fragmentary discharges consisted in both areas of fine 
dust and gravelly detritus of small lapilli, which were 
not ejected in such quantities as entirely to conceal 
the ordinary non -volcanic sediment of the water- 
basin. The dust and cinders mingled with the red 
sand and angular scree-material, so that we now see a 
group of red, somewhat ashy sandstones and breccias. 
Among the component fragments of the breccias, 
a considerable variety of igneous material may be observed. While the 
111 ost of the non-volcanic stones may have been derived by ordinary processes 
°1 weathering from rocks exposed at the surface, it is by no means improb- 
able that some of them, including even pieces of Culm grit, killas and baked 
slate, may have been ejected from volcanic vents. 1 
Taking the volcanic rocks of this district as a whole, I regard them as 
re mere edges of sheets that have flowed from vents which not improbably 
re concealed somewhere along the centres of these old Permian valleys, 
t 7 Vlsible necks have ,)een described from any part of the area, and though 
have not examined the whole of it, nothing of that nature was detected by 
ue either m the Crediton Valley or between Silverton and the Exeter 
eighfiourhood. The Tiverton district, which has not yet been searched, 
‘Ppears to be the only tract where any chance remains of finding some of 
the vents. ° 
Fig. 2.31. — Section of ag- 
glomerate overlain with 
sandstone and andesite, 
Fosbury, Crediton. 
o indication of any sills has been met with among the Devonshire 
iniun rocks. None ol the lavas which I have seen have the internal 
aracters of true sills, while in the field their association with the sand- 
nes and breccias in no observed case points to intrusion. 
aeon t Ugl1 mUCh r6mains t0 be doue in tllis re gion before an adequate 
Unt cau be given of the interesting series of eruptions which concludes 
volxS t nL C nT P ° S in i0n m!' the Devonshire breccias see Ml - R- N. Worth, Quart. Journ. Gcal. Soc. 
die neck of » 1’, ’’i 9 ; T " S aUth ,°? llas ado t lted thfi view that the granite of Dartmoor represents 
evidence q PPm S ? at VO | U! “° from whlch these later volcanic materials were ejected. But all the 
lavas as i “ faV0Ur of numemis sma11 vents situated not far from the outcrops of the 
1'. 498 Tl 6 tv U1 the t6Xt ' See Mr ' B ' Hobson > Q mrt - Durn. Gcol. Soc. vol. xlviii, (1892), 
evidence b«V “ v” granite 18 later than tlle «UTom$ng Carboniferous rocks, but no good 
been obtained to connect it with the Permian volcanic phenomena of Devonshire. 
