358 Rev. Mr, Conyheare on the [April, 



more abundant in coralloids is found yet nearer in the nei^h»- 

 bourhood of Lindridge. The limestone also of Bickington, near 

 Ashburton, contains many of these fossils. The fragments of 

 the ^reywacke class may readily be traced to the rocks of that 

 species which lie in most places immediately beneath the marie, 

 ^and with which indeed the transition limestones of the country 

 are interstratified. Of the granitic and porphyriiic fragments, 

 those marked A, 1, 2, 3, have all the characters of a rock fre- 

 quently occurring on the confines of the .Dartmoor granite, and 

 not unfrequently intermixed either as veins or irregular masses, 

 both with that rock and with the neighbouring schistus. It wiU 

 be found thus distributed a little beyond Bovey Tracey. I have 

 met with aggregates nearly similar at the junction of granite 

 and schist at Ivy Bridge, and at Buckland in the Moor. The 

 remaining felspathic fragments I have little hesitation in refer- 

 ring to that class of rocks which are known by the name of 

 Elvans, and found in numberless instances traversing the metal- 

 liferous slate of Devon and Cornwall. In the latter county^ 

 they have been more frequently observed, both from the greater 

 extent of those sections of the Killas which are offered by its 

 coasts, and the frequency and magnitude of the excavations made 

 by the miner. In Devon I have noticed them near Tavistock, 

 near Buckland Monachorum, and in the course of the West 

 Okement, and have no doubt that they might be detected in 

 Viarious other quarters, especially near the junctions of the granite 

 and slate. The only instance of dissimilarity which 1 have 

 observed is the occurrence in some cases of large crystalline 

 masses of the felspar, which I have termed semi vitreous, and 

 stated to form a part of the rocks marked D I, 2, 3, 4. My 

 limited collection of Elvans does not afford any analogous spe- 

 cimen, but when we remember that nearly every mine in Corn- 

 wall presents one or more varieties of this rock, and how endless 

 are the minute shades of difference which characterize them, it 

 will, I think, be allowed that there is nothing improbable in the 

 supposition that the whole contents of this breccia have been 

 furnished by the inferior rocks of its immediate neighbourhood, 

 by those, perhaps, whose edges are yet covered by it at a depth 

 to which our labours and investigations have but little chance 

 of penetrating. 



You will scarcely need to be reminded that Mr. Leonard Hor- 

 ner arrived at a like conclusion from his examination of the 

 rock marie and adjacent strata in Somersetshire.* It struck 

 me as singular that among the fragments which fell under my 

 inspection I observed no traces of hornblende rock, or green- 

 stone, although the latter especially, and in some instances 

 small portions of the former are to be found on the borders of 

 Dartmoor. The cliffs of Henoch present so large and striking 



• Siee GeologicalTransactiong, vol. iiL 



