64 Geological Society: — On a 



tion (from want of time) to the northern part of the forest than to 

 the rest. This district has during the last two years engaged their 

 special attention. They had provisionally retained the name quart- 

 zite for the rocks exposed about Blackbrook &c, probably the lowest 

 visible on the forest. This name proves to be inappropriate; and 

 they propose to call the group, which contains much fine detrital 

 volcanic material, the Blackbrook Series. They have also reason to 

 believe that the anticlinal fault is less than was supposed, and that 

 we have here a fairly unbroken base for the forest-rock already 

 described. In this case there ought to be representatives of the 

 great agglomeratic masses on the western side of the anticlinal 

 (High Towers &c). The authors believe that they have found 

 these, though as much finer and more waterworn detritus, in the 

 greenish grits above Longcliff and Buckhill. The authors also 

 believe that they have succeeded in tracing a coarse agglomerate 

 with slate fragments round about three fourths of the circumference 

 of the forest. Further notes upon the district of Bardon Hill, 

 Peldar Tor, and Sharpley are given; and the origin of the remark- 

 able rock of the last, so like some of the Ardennes porphyroids, is 

 discussed ; the authors believe it to be a volcanic tuff, altered by the 

 passage of water or of acid gases. Descriptions of the microscopic 

 structure of some of the rock fragments included in the coarse 

 agglomerate and of some of the slates are given. Also a notice of 

 two small outbursts of igneous rock, of the northern syenite type, 

 previously unnoticed are mentioned. 



2. " On the Geological Age of Central and West Cornwall." By 

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



The author divided the stratified rocks of this district into four 

 groups, as follows : — 



1. The Fowey Beds, mostly soft shales or fissile sandstones, with 

 some beds of roofing slate ; no limestones or conglomerates. These 

 beds cover an area of not less than eighty square miles, and contain 

 numerous fragmentary fish-remains and other fossils, many as yet 

 undetermined, the whole, however, indicating that the beds are 

 either Lower Devonian or Upper Silurian. The strike of the beds 

 is X.W. to S.E. ; and they are estimated to be not less than 10,000 

 feet thick. 



2. The LadocJc Beds, consisting of slaty beds, sandy shales, sand- 

 stones, and conglomerates ; no limestones and no fossils. They 

 cover an area of more than 100 square miles to the west and south 

 of St. Austell, strike from east to west, and overlie Lower Silurian 

 rocks unconformably. They are estimated at from 1000 to 2000 

 feet thickness. 



3. The Lower Silurians consist largely of slates and shales, with 

 some very thick conglomerates (one being at least 2000 feet thick), 

 some quartzites, and a few thin beds of black limestone. The 

 quartzites and limestones have yielded fossils (chiefly Orthidce) 

 which are pronounced to be of Bala or Caradoc age by Davidson 

 and others. The total thickness of these beds is estimated at 



