896 Machintosh — Railivay Geology in Devon, 



sembling an old tidal zone, which has been intersected by the sub- 

 sequent excavation of valleys. The railway cuts through a series of 

 the remaining ridges and platforms, revealing the same bed at dif- 

 ferent levels (See Plate XYIII. Fig. 3, a drift, h slate, c railway). 

 Many of the boulders are more than three feet in diameter. 

 Most of the stones are much rounded and often polished. The 

 drift exhibits no order in the arrangement of the stones, which 

 lie at all angles, and sometimes enclose lenticular patches of sand. 

 It bears no resemblance to river- shingle, supposing a river could 

 have distributed so great a quantity of drift over so large an area.' 

 The size of many of the stones, the signs of violence apparent in 

 the pell-mell heaping together of materials, and the extent of sur- 

 face covered, render it certain that no tranquil lake could have de- 

 tached, transported, and accumulated this drift. It seems only 

 explicable by the action of the sea during a gradual rise of the land. 

 The stones consist of an extremely hard yellowish-white igneous 

 rock, a hard and dark-coloured rock, quartz, pebbles with quartz 

 veins, etc., — all indirectly local. The first railway -cutting north- 

 west of Bovey station is through a crumbling shale or slate 

 (Carboniferous ?) capped by boulder drift. Cutting No. 2 is through 

 a plateau covered with six feet of drift. The slates underneath have 

 been shaved off, in some places broken off, and re-arranged. No. 3 

 reveals a great thickness of drift in regular layers. In No. 4 the 

 shale, slate, or whatever it may be called, exhibits a whitened or 

 baked appearance, in which the stratification is often lost. In places 

 it resembles trap. In No. 5 the rocks are much stained with oxide of 

 iron, and only thinly covered with drift. Farther on the drift, with 

 stones 3^ feet in diameter, re-appears under a covering of angular 

 detritus. In No. 6, under a great thickness of slaty detritus, the 

 drift resembles some of the raised beaches on the Cornish coast. In 

 some places it has become consolidated. It coiatains numerous 

 rounded and polished botdders of yellowish-white igneous rock. In 

 No. 7 the drift still shows itself, covering an indescribable kind of 

 rock, consisting of shale, graduating into the hard dark-coloured 

 stone, which has largely supplied the boulder drift. Dykes or veins 

 of a yellowish- white igneous rock (Elvan?) here make their appear- 

 ance. In No. 8 there is a fine display of the junction between slate 

 and an erupted mass of j'^ellowish- white igneous rock with dark specks 

 (PI. XVIII. Fig. 4, a igneous rock, &, 6 slate). As the ground has 

 obviously been lowered by a great amount of denudation, the observer 

 may be cautioned against regarding the right and left hand pro- 

 jections of the igneous rock as superficial overlaps. In some places 

 the shale close to the erupted mass has undergone little or no 

 alteration.^ 



^ At a lower level, by the side of the railway, a deposit of much finer gravel may 

 here and there be seen, part, if not all, of which may be river shingle. 



2 This igneous rock I at first took for a fine-grained granite, and on the Geological 

 Map it seems to come within the granite area. I saw afterwards a stone on the road- 

 side to the east of the Blackenstone rock, one part of which consisted of this rock 

 separated by a straight and very distinct line from the other part, which was very 

 decided granite. In the present unsettled state of petrology, it is perhaps better to 

 be cautious in applying names. 



