68 report— 1877. 



Note on the Serpentine of Duporth, in St. Austell Bay, Cornwall. 

 By J. H. Collins, F.G.S. 



In this paper the author shows that an intrusive Greenstone rock, extensively 

 worked for road-stone at St. Mewan, near St. Austell, is, within 3 miles of that 

 place, converted into a Porphyritic Serpentine, and believes that this change has 

 been effected by the agency of mineral solutions acting through fissures from 

 below. 



On the Drift of Plymouth Hoe. By J. H. Collins, F.G.S. 



The author stated that excavations were nearly always going on in the neigh- 

 bourhood of Plymouth Hoc, and that fresh sections of the so-called liaised beaches 

 and Glacial deposits were continually being exposed. 



He had lately visited the Hoe, Mount Batten, and Deadman's Bay, in company 

 with Mr. Whitley, of Truro, and had found gravels, sands, and clays lying in the 

 hollows of the limestone and filling fissures and caverns. The gravels were some- 

 times cemented by stalagmite into a conglomerate. The pebbles were composed of 

 quartz, limestone, tourmaline and schist, greenstone, blue and red grit, hard clay- 

 slate, schorl rock, granite, elvan, flint, chert, stalagmite, and one pebble of granite, 

 all of which the author considered had been derived from the rocks of the neigh- 

 bourhood within a few miles. None of the pebbles were in the least degree ice- 

 scratched, and there were very few angular fragments of any kind. 



The gravels had yielded bones of Bhinoceros, Elephants, and other animals of 

 the so-called Mammoth period. 



The author discussed the evidence of local denudation, and arrived at the fol- 

 lowing conclusions : — 



1. The deposits are not raised beaches. 



2. They are not glacial. 



3. They were formed rapidly. 



4. Gravels, fissure deposits, and cave deposits are of the same age. 



5. That they belong to the Mammoth period. 



6. There is no evidence in the immediate neighbourhood to carry back their for- 

 mation more than a few thousand years. 



Note on the Correlation of certain Post-Glacial Deposits in West Lancashire, 

 By C. E. De Eance, F.G.S., of H.M. Geological Survey. 



_ The valley of the Pibble, at Preston, is entirely excavated in Glacial drift, con- 

 sisting of Boulder-clay, with an included bed of sand and shingle, together reaching 

 a thickness of between 150 and 200 feet. At the bottom of the valley is a broad 

 alluA'ial plain through which the river swings in a series of S-like curves, denuding 

 away the sides of the valley, and forming them into steep cliffs where the convex 

 curves of the S touch the margin of the valley, on the slopes of which are left frag- 

 ments of old river-terraces, marking the former position of the Ribble before it had 

 vertically denuded as low as at present. 



The terraces, as well as the lowest alluvial plain, generally exhibit the following 

 sequence of deposits : — 



1. Fine alluvial silt and loam. 



2. Peaty beds and trunks of trees. 



3. Large gravel and stones washed out of the drift. 

 Marking: — 1. Alluvial deposit from floods. 



2. Obstruction of drainage. 



3. Denudation. 



Throughout Western Lancashire an extensive plain occurs often below the sea- 

 level, covered with peat often 30 feet in thickness, and descending to a depth of 

 some 60 feet beneath high-water mark — a depth sufficient, if the district was ele- 

 vated to that amount, to connect Cumberland with the Isle of Man, in which, as in 



