PENGELLY — ON THE AGE OF THE DAETMOOlt GRANITES. 17 



Dr. Daubeny pointed out to mc certain pebbles, which he thought 

 granite, in the red conglomerate at Livermead, in Torbay ; my own im- 

 pression, however, is, that they are trap. I do not, of course, sup- 

 pose that my opinion would be of any value when opposed to that of 

 the eminent man just named, especially on a point of this kind. I 

 merely mention the fact, to show that I have not allowed a strong 

 bias, supposing me to have one, to overrule my judgment; or I should 

 have quoted the Livermead pebbles as granitic, on Dr. Daubeny's 

 authority. 



But waiving this point, I cannot regard it as certain that the red 

 rocks of Torbay and of the South Devon coast generally are entirely 

 destitute of Dartmoor detritus. Every one who has paid attention 

 to the sandstones there, must be well aware that in many cases they 

 are eminently micaceous ; this is very noticeable at the Corbons and 

 Livermead Head, in Torbay, where every newly exposed surface 

 glistens with an almost metallic glance, from the presence of nume- 

 rous large scales of black mica; doubtless a result of the destruction 

 of a large amount of pre-existing rock, of which mica was a consti- 

 tuent. It is, no doubt, true that certain gritty members of the older 

 rocks of the county sometimes contain scales .of mica ; it seems im- 

 possible, however, that these can have been the source of those found 

 in the Bed Sandstone, for, so far as I am aware, they are, in the first 

 place, always small instead of large ; and, in the second place, in- 

 variably white instead of black. On the other hand, in a passage 

 already quoted from Sir H. De la Beche's " Beport," it is stated that 

 the mica of the Dartmoor granite is sometimes black. Nor is it 

 difficult to understand that whilst pebbles and boulders might be 

 unable to force a passage to what is now the South Devon seaboard, 

 comparatively small thin flakes of mica succeeded in accomplishing 

 the journey. The fact, however, that nodules of micaceous trap occur 

 in the conglomerate, renders it manifestly unsafe to insist on the 

 granitic derivation of the scales in the sandstone. 



If it be true that granite pebbles occur at Sampford Courtney, 

 North Tawton and Haldon, but do not exist on the southern coast 

 of the county, — in other words on the north and north-east, but not 

 on the east, of Dartmoor, — may we not have, in this fact, an indication 

 of the prevailing direction of the most powerful currents, or other 

 agents of transportation, in this part of modern Devonshire during 

 the Bed Sandstone era ? 



The following appears to be a strikingly parallel case. The low 

 plain known as Bovey Heathfield, in Devonshire, is covered with a 

 very coarse gravel, and surrounded, on almost every side, by hills of 

 considerable elevation ; on the north and west the granite heights of 

 Dartmoor, fringed with traps and metamorphic rocks ; on the north- 

 east and east the greensand hills of the Haldon s, capped with vast 

 accumulations of flint and chert; and on the south a range of hills, 

 extending from Newton towards Ashburton, consisting of Devonian 

 limestone and associated rocks. The Bovey graved consists almost 

 entirely of Dartmoor material, a flint or chert fragment occurring 



VOL. VT. D 



