518 Geological Society : — 



April 30th.— Prof. Charles Lnpworth, LL.D., F.R.S., 

 President, in the Chair. 

 The following communications were read : — 



1. 'The Origin and Associations of the Jaspers of South-eastern 

 Anglesey.' By Edward Greenly, Esq., F.G.S. 



Eed jasper and jaspery phyllite are widely distributed in the 

 southern and south-eastern parts of Anglesey, in the districts of 

 Xewborough, Pentraeth, and Beaumaris. They are associated with 

 limestones, diabases, serpentines, and with grits and shales. They 

 have been much modified by earth-movements, which have pro- 

 duced brecciated and schistose structures ; but where original struc- 

 tures have survived, the true relations of the rocks can often be seen. 

 The diabases have the same characters as the pillowy and variolitic 

 rocks so often associated with radiolarian cherts and jaspers in 

 many parts of the world, and at several different geological horizons; 

 and the relationships of the jaspers and igneous rocks resemble those 

 seen in the radiolarian cherts of Southern Scotland. It is inferred 

 that the jaspers are altered radiolarian cherts. The evi- 

 dence for the age of the group is inccmplete. There is not sufficient 

 evidence to refer it to the Arenig Series, and it is possible that it 

 belongs to an altogether different period. Its relation to the crys- 

 talline schists of the region is obscured by conflicting evidence : one 

 chain of reasoning leads to the view that the group is older than 

 the schists, and has been involved in their metamorphism : while 

 another gives strong reason for supposing that it is of later date. 



2. ' The Mineralogical Constitution of the Einer Material of the 

 Bunter Pebble-Bed in the West of England.' By Herbert Henry 

 Thomas, Esq., B.A., F.G.S. 



Specimens were collected at intervals, from Budleigh Salterton, 

 in Devon, to Eitzhead near Milverton, in Somerset, and other sands, 

 for comparison, were taken from the red rocks above and below. 

 After treatment with acids, to remove iron-oxides, the sands were 

 separated by heavy liquids into three parts : — 



(a) Heavy residue : specific gravity exceeding 2*8. 



(b) The bulk of the quartz. 



(c) The lighter part, with most of the alkali-felspar. 



The sands, on the whole, contain a very small percentage of 

 minerals with a specific gravity of more than 2*8; while the pro- 

 portion of material over, to that under, 2-58 is about 70 *or 80 to 30 

 or 20 per cent. A list and description of twenty minerals found in 

 the sands is given, with, in some instances, the chief characters by 

 which they were identified. The compound grains include felsite, 

 quartzite, chert, shimmer-aggregates, leucoxene, and other decom- 

 position-products. The gradual decrease in the percentage of heavy 

 minerals from Budleigh Salterton to Uffculm indicates the carriage 

 of sediment by a southerly current, and this view is strengthened by 

 the decrease in staurolite and a gradual diminution in the size of the 

 tourmaline-grains. The increase in proportion of heavy grains from 

 Uffculm to Milverton, and the further decline northward, together 



