587 



hills, and is sometimes worked far roofing-slate. It contains bands 

 of limestone of a peculiar character. Organic remains occur only 

 in the upper part, and agree apparently with those of the " great 

 limestone." 



5 . Lowest Band of Limestone. — The limestone between Staper-hill 

 and Bickington, and on the highway road by Goodstone to Ashburton 

 and Buckfastleigh, is assigned to this portion ; also that of Chudleigh, 

 and the limestone at the base of Great Haldon is perhaps of the same 

 age. The organic remains consist of corals and shells. Thin seams 

 of carbonaceous matter also occur. 



Igneous Rocks. — These formations consist of granite, porphyry, 

 and trap. The granite of Dartmoor was shown in 1836, by Prof. 

 Sedgwick and Mr. Murchison, to be more recent than the carbonife- 

 rous strata ; and Mr. Austen adopts the same view, as veins of gra- 

 nite penetrate the culm beds at Higher Alway and Lower Alway, 

 near Bovey. The principal mass of Devonshire granite has in some 

 places a height of 1800 feet, but over the whole of its area there is 

 not the slightest appearance of any stratified deposit. The granite 

 of Dartmoor is considered by Mr. Austen to be of different ages, 

 as veins of coarsely grained are intruded among the common varietj^. 

 Blocks of hornblendic granite are said also to occur, imbedded in 

 the true granite ; and in some places the granite is so felspathic as 

 to resemble trachyte. 



Trap Rocks — The author describes, with some detail, the horn- 

 blendic trap dyke of Wear, and shows that it must have been irrupted 

 subsequently to the deposition of the chalk, because fissures in the 

 limestone, traversed by the dyke, are filled with fragments of various 

 formations, including chalk, and are charged with manganese, an 

 effect produced by the intrusion of hornblendic trap throughout this 

 part of Devonshire. 



In the parish of Kington, veins of trap, on approaching the granite, 

 are said to become more compact, and in the proximity of it, to be 

 distinctly crystalline. Associated with the culm strata are bedded 

 traps, apparently of contemporaneous origin ; but the close of the cul- 

 miferous period is stated to have been marked by irruptions of the 

 porphyry found at Pocombe-hill, and other places near Exeter. At 

 Western, in the parish of Ide, it rests upon the culmiferous shale ; 

 but Mr. Austen says, it might be considered to rest on the new red 

 sandstone, as that formation flanks the base of the hill. In the quarry, 

 however, where the porphyry is worked, it has been cut through, 

 and found to rest upon shale. This rock has contributed largely 

 to the formation of the conglomerates of the new red sandstone. 

 Trap dykes are very common among the older slates, and have pro- 

 duced decided effects on them, and the general features of the 

 country. Their age the author does not attempt to define ; but from 

 their being more abundant in the older than in the newer rocks, he 

 conceives that they may have been, in part, irrupted before the latter 

 were deposited. In the coast section, beds of hornblendic trap are 

 included in the transition shale, to which they adhere by the lower 

 surface, but not by the upper. Similar, imbedded, trappean rocks 



3 A 



