398 Mackintosh — Railway Geology in Devon. 



of rain-water. Whether the foliation coincides with original lamina- 

 tion is a question for the petrologist. 



"Boss and Tail," near Moreton-Hampstead. — This town is sur- 

 rounded with many projections of granite which throw some light 

 on the later denudations of the earth's surface. The Blackenstone 

 Eock (about 2^ miles to the east) is one of the most striking granitic 

 bosses in Europe. On account of its elevated position it can be 

 seen from a distance of many miles round. The north-west side 

 must be nearly 200 feet high. The most projecting part of this 

 boss consists of cross-jointed hard granite. It has been rounded 

 totally irrespective of structure. A close inspection will show that 

 rain has only roughened its surface. It has been swept clean of 

 debris all round, excepting a few stones on the north side. On the 

 north-east side it graduates into a tail which presents a very strikingly 

 smoothed and rounded appearance. If ice has not been here, there 

 would seem to be little necessity for supposing it to have been any- 

 where. There are no distinct striations; but an iceberg, without 

 stones in its base, would not have striated it, or supposing striations to 

 have occurred, granite is about the worst rock in the world to have 

 preserved them. Here the tail is ia front (" upstream "), but this is 

 generally the case with glacial bosses and tails. Plate XVIII. Fig. 7 

 will give some notion of the appearance presented by the tail, with 

 the boss fore-shortened, as seen from the north. Nearly all over the 

 undulating table-land between the Teign valley and Dartmoor, com- 

 monly so-called, there are rounded, smoothed, and levelled surfaces 

 which can be best explained by ice-action. 



Boch-basins. — A great number of rock-basins may be found within 

 a few miles of Moreton-Hampstead. Geologists would do well to 

 visit the Druid's altar (near the Blackenstone Eock) before it is quite 

 quarried away — before its rock -basins are exploded by gunpowder, 

 and its "ribs of beef" chopped up. The latter term is applied to 

 six or seven ridges and furrows running down both sides of the 

 summit of the rock. Though rain is roughening the ridges, it is 

 certainly not forming the furrows, which are covered with moss. On 

 this and neighbouring parts of the rock there are many basins. One, 

 very regular and smooth-sided, is partly filled with grass-covered soil. 

 On the north side of the rock there is a double basin which slopes 

 (see Plate XVHI. Fig. 8) towards the brink of a precipice. In other 

 places there are small deep, round, smooth basins like pot-holes on the 

 sea-coast, or in the channel of a river. In one of these I observed the 

 rain-water in a state of gyratory motion ; but the round form was 

 evidently the cause, not the effect, of the whirling of the water. On 

 Hell Tor (commonly called Heltor Eock) there is a very large basin 

 (at least 6ft. in diameter by 3ft. deep), one side of which is of a 

 perfectly semicircular form, evidently hollowed out by a forcible 

 agency. It is broken down on one side by a rent, so that it can hold 

 no rain-water. There are many small basins on the top of this tor. 



Origin of Bock-hasins. — Mr. Ormerod, F.G.S., of Chagford, the 

 principal writer on rock-basins, seems to follow Dr. MacCulloch and 

 other early geologists, in attributing all rock-basins to atmospheric 



