63 REPORT — 1841. 



nite veins in the bed of the Erme river, above Ivy Bridge, of which he exhibited a hori- 

 zontal section. He at first regarded them as veins which had been injected into the 

 yielding joints and fissures of the fine jaspery grit rock ; closer inspection showed him 

 also certain very delicate threads of the same flesh-coloured granite, emanating from 

 the larger joints, but ranging after the planes of deposition of the grit ; and the jas- 

 per rock was no more dislocated there than elsewhere. Higher up the river-bed he 

 came to what appeared a hard junction between the grit and the granite ; the former 

 Avas in a highly metamorphic condition, but its upper surface showed frequently that 

 its laminae of deposition had not been obliterated. Specimens of the altered rock, 

 obtained from the immediate confines of the hard junction line, showed no mineral 

 transition between the granite and the altered grit. He had observed below, that 

 while the grit showed no evidence whatever of having been acted on by any unusual 

 violence, most of the granite veins ranged in the direction of its normal joints. 

 Almost the first specimen he obtained from one of these joints (upwards of four feet 

 above the granite in mass) showed its walls to be perfectly granitified, the granitic 

 matter shading out laterally in the most delicate pencillings, while nearly all the other 

 joints afforded the same evidences of conversion, in a greater or less degree. From 

 these facts Mr. Williams felt constrained to deny that the granite had ever been for- 

 cibly injected, and to infer that the entire phsenomena might be better explained by 

 tranquil fusion and conversion. He contended that the pre-existing sedimentary 

 rock had been reduced and converted into granite by intense heat from within, tra- 

 versing the joint-lines in their several directions, and radiating from them laterally 

 among the laminae of deposition, apparently indicating, that wherever the temperature 

 amounted to its point of fusion, there the rock would be reduced to the same condi- 

 tion with the incandescent mass below. With regard to the elvans or greenstones, 

 and the so-called clay-slate or killas, he considered that abundant evidence existed 

 in Devon and Cornwall to show that they also Were volcanic products, the former id 

 their usual amorphous type, the latter in a stratified condition. On the shore of the 

 Padstow estuary, west of Wadebridge, fourteen of these elvans might be observed at 

 varying intervals, each one underlaid and overlaid by volcanic breccia, grit, ash and 

 clay-slate : these greenstones all observed the same angle of dip, and precisely the 

 same strike as the killas above and below them ; indeed several of them are disclosed 

 on the opposite side of the river, in the precise places which the direction of strike 

 would have indicated, and there also tilted up at the same angle with the clay-slates 

 above and below. This line of low cliif extends about a mile, the slates and elvans 

 having a permanent southern dip, with one undulating exception. There, fourteen 

 submarine lava-streams occupy perfectly distinct levels in the vertical scale, each one 

 representing its own period of eruption, during a greater or less interval of time, 

 and each one apparently preceded or accompanied by ejected fragmentary matter — 

 by grit, ashes and mud, the greenstones being very commonly based upon a grit or 

 breccia, at other times upon an ash or slate, each of them appearing to pass insensi- 

 bly into the other. Mr. Williams particularly directed attention to the coast round 

 Saltash, in the immediate vicinity of Plymouth, or from Redding Point to the great 

 mass of porphyry near the fishing-houses, which was one uninterrupted series of va- 

 rieties of volcanic ash, oftentimes passing into clay-slate, interstratified among the 

 thick red sandstone beds seen on the east and west cliff's of the Sound. The lower 

 beds of this sandstone Mr. Williams observed to be traversed by four north and south 

 dykes, which cut the beds at right angles, and filled with the same rejectamenta that 

 he had observed to constitute the partings between the sandstone beds ; these he sup- 

 poses may have been the vomitories through which the mud or ashes were blown out, 

 as it was an interesting fact, that these ash-dykes did not traverse the more southern 



beds, but were overlaid and concealed by them. 



• 



On the discovery of Organic Remains, in a raised beach, in the Limestone 

 Cliff under the Hoe at Plymouth. By E. Moore, M.D., F.L.S. 



The raised beach discovered under the Hoe by the Rev. Richard Hennah, has 

 lately, by the extension of the quarry near which it was situated, been almost en- 

 tirely removed, and in the progress of the work, it was ascertained to occupy a de- 

 pression in the face of the limestone cliff, 100 feet wide and forty deep : its base is 

 thirty-five feet above the present sea at high water spring tides ; it runs upwards and 

 backwards twenty feet, inclining inwards with the slope of the rock, and is covered by 



