40Q Mackintosh — Railway Geology in Devon. 



witliin a given period; the natural edifice must have received its 

 last touch v^hen Dartmoor last rose above the sea; and, since the 

 final embrace of the denuding agent, the powers of the air have not 

 had time to mar the general effect. On one side of some tors the 

 assailed blocks must have been carried clean away in a manner that 

 ice will not account for, and which is altogether inexplicable on the 

 subaerial theory. In the vicinity of other tors we find heavy blocks 

 of granite out of place, and piled on blocks likewise out of place, on 

 nearly level ground, — a phenomenon to which a mere wasting, trick- 

 ling, dribbling agency, such as rain, could never have given rise. 

 Many cleanly-cut passages through the tors have evidently been left 

 by a wholesale clearance of blocks, and where these are wanting, 

 the indentations, inlets, and incipient caves point to the insinuating, 

 disentangling, and removing agency of breakers. The smaller 

 crevices are not always, as has been imagined, the elfect of enlarge- 

 ment of fractures by rain, and, therefore, stages in the passage- 

 forming process, but often the original fractures themselves with 

 their rain-proof sides minutely corresponding. 



Mock-pillars. — Among the tors of Dartmoor there are many rocky 

 projections, more or less regular, to which this term may be applied. 

 Bowerman's Nose, near Manaton, is perhaj)s the most striking. The 

 impression it must leave on an unbiassed mind is that a powerful 

 cause has carried away the blocks by which it was once surrounded. 

 Nothing seems more obvious than that the denudation must have 

 been equal to the removal of whole blocks, and not merely of chips 

 or grains. In the case of this and other rock-pillars, there are no 

 indications of the parts removed having been softer than the parts 

 left unscathed. Indeed, the path of denudation appears sometimes 

 strewn with the very blocks which once composed the massive 

 structure, of which the pillar is the only part now remaining in situ; 

 and these blocks are often in positions where they could not have 

 fallen, and where, therefore, they must have been carried. 



In illustration of the above remarks on the rocky projections of 

 Dartmoor, it may be stated that the Hountor Eocks consist of a series 

 of cliffs formed by the removal of whole blocks, and roofless caves from 

 one to three blocks wide, from which whole blocks must have been 

 abstracted. The two Hey Tors (which may be seen at a distance of 

 ten miles from the railway at Newton) exhibit similar phenomena, 

 but they are principally remarkable for the evidence they present 

 of the denuding agent having come from the south-south-east^ — 

 smoothed the projecting masses up an inclined plane — stripped bare 

 the sides — and scattered myriads of blocks and fragments towards 

 the north-north-west along a slightly-inclined surface, the contour of 

 which, from a distance, presents a perfectly straight line.'^ How far 



^ Since -writing the above, I have found that the ingenious author of " Frost and 

 Fire," briefly mentions the Hey Tor Eocks as having been denuded by ice float- 

 ing from the north-east, without referring to the direction of the tails and scattered 

 wrecks. He likewise notices the ice-ground contour of the Blackenstone Rock, but 

 leaves its tail out of consideration. 



2 These blocks and fragments consist of, at least, two kinds of granite : a reddish 

 fine-grained variety, and the common coarse-grained variety with large oblong 

 crystals of felspar. 



