Geology of the South-east of Devonshire. 475 



with reference to such views. At all the above localities the porphyry rests on the undisturbed 

 surface of the carbonaceous shales. A quarry yielding a very compact variety of the rock is worked 

 on the summit of a hill at Western, in the parish of Ide : in this instance (one of those I believe adduced 

 in proof of the association of the porphyry with the new red sand formation) the igneous rock would ap- 

 pear to rest upon the carbonaceous deposit, of which the lower part of the hill on every side is composed. 

 The entire thickness of the porphyry has been cut through, and here, as elsewhere, it rests on carbona- 

 ceous shale ; a section exhibited in a lane leading down to the stream near Dunchideock Bridge, 

 might seem an exception to the above, and place a thick mass of porphyry within the new red sand- 

 stone ; but I believe it to be the result of a small fault running parallel with the stream, and which has 

 let down a portion of the porphyry to the west. As yet, I have seen no unexceptionable example of 

 the Exeter porphyry resting on beds of new red conglomerate, but instances are abundant where the 

 conglomerate rests on the abraded surface of the porphyry ; and it must be remembered that the blocks 

 of porphyry which enter so largely into the composition of the lower conglomerates, prove that the por- 

 phyry had cooled down into a crystalline mass before the production of the conglomerate commenced. 



It will be seen, therefore, that this rock rests upon carbonaceous shales, and hitherto has not been ob- 

 served to cut through them. It is found only in detached masses, placed at very different elevations, owing 

 to the subsequent disturbances which have affected the district ; and it has contributed largely to the 

 sedimentary beds next in sequence to those on which it rests; and these reasons induce us to consider 

 the few remaining portions of the rock as evidences of an extensive submarine eruption of felspathic 

 lava which took place at the close of the carboniferous period, and long before the production of the 

 lowest beds of the Exeter conglomerate. 



The most recent trappean rock, so far as age can be established by association 

 with beds of ascertained relative antiquity, is that of Wear. The experienced geo- 

 logist is here quickly stimulated to look for those causes which produced the 

 masses of crystalline hmestone, jasper, and blocks of fused and altered rocks scat- 

 tered over the surface of the soil, and built into all the walls, particularly in the 

 vicinity of Bishopsteignton. A portion of the erupted trappean matter which has 

 caused these appearances has been cut through longitudinally by the road from 

 Teignmouth to Kingsteignton. In this section, the mass nearest Lower Wear is 

 compact, and traversed by veins of quartz ; about one hundred yards further on, is 

 an included bed of hard and splintery slate, about fifteen feet thick ; to the north 

 of the road are several quarries, and in one of these the trap rests on the edges of 

 limestone. Above Higher Wear included angular blocks of trap first appear, which 

 in a short distance become so numerous as almost to form a conglomerate cemented 

 by a trappean base ; in a quarry at the east end of the section the trap assumes a 

 columnar structure, and is very compact. By the map, PI. XLI., the trap is seen 

 to be the axis of a ridge, which has a direction from north-east to south-west ; 

 with slates and limestone resting against it on each side. The dyke can be traced 

 by Colway Cross up to Rowdown Cross, a little beyond which it enters the new 

 red sandstone : in the contrary direction it is just covered by a low rounded hill 

 of shale, from beneath which it reappears at the level of the Teign at Clay-cellars : 

 and on the opposite bank, owing to a fault in the direction of the valley, it forms 



