620 MR. H. H. THOMAS ON THE MINERALOGICAL [ Nov. 1902, 
32. The Mrneratoeicar Constrrurion of the Finer Marertrat of the 
Bunter Prspie-Bep in the West or Enetanp. By Herserr 
Henry Tuomas, Esq., B.A., F.G.8. (Read April 30th, 1902.) 
[Puates XXXT & XXXII] 
ConTENTS. 
T, Imtroduction. 1... .0esee.bsuie eens ote eaenes oseeaee eee eae aaa eee 620 
II. Petrography of the Sands: Description and Distribution of the 
Mineral Species......d.cn.. s-cee.sueis sen deoe nes Joe ve See eee eee Reet 620 
III. Possible Directions of the Sediment-bearing Currents, and 
Sources of the Mineral-Grains 5.2... 5.2.0202.5..2.sc-e. 2g 628 
{Map on p. 629. ] 
I. InrrRoDvctTIon. 
Mvcu work has already been done on the pebbles and larger 
tragments of rock of the Budleigh-Salterton Pebble-Bed, but little 
or none on the finer material forming the matrix of this most 
interesting deposit. It occurred to me that a microscopic investi- 
gation of this finer material might bring out a few points of geological 
as well as mineralogical interest. Therefore it has been my en- 
deavour to make as complete a mineralogical analysis of the sands 
as possible. 
Specimens were collected at intervals along the strike of the 
Pebble-Bed, from Budleigh Salterton on the southern coast of Devon 
to Fitzhead, north of Milverton, in Somerset; other sands, for com- 
parison, were taken from the Red Rocks above and below. 
After treatment with.acids, so as to remove the coating of iron- 
oxides from the grains, the sands were separated by means of 
heavy liquids into three parts :— 
(a) Heavy residue, with a specific gravity greater than 2°80. 
(b) The bulk of the quartz; and 
(c) The lightest part, with most of the alkali-felspar. 
Il. PrrroGRaAPHy oF THE SANDS : DESCRIPTION AND DISTRIBUTION 
OF THE MINERAL SPECIEs. 
At the southern end of the outcrop of the Pebble-Bed, the matrix 
consists of incoherent material, each sand-grain being covered with 
a coating of red iron-oxide. On tracing the deposit northward, 
however, to the borders of Somerset, the bed loses much of its red 
colour, and in this area, owing to the presence of many masses of 
Culm-Measure limestone in the vicinity, the grains are cemented in 
a calcareous matrix, the deposit ultimately taking on the form of 
the Dolomitic Conglomerate. 
The sands contain, on the whole, a very small percentage of 
mineral-grains the specific gravity of which is greater than 2°80; 
while the ratio of material over 2°58 to that under 2:58 is about » 
70 or 80 per cent. to 30 or 20 per cent. In some cases the 
heavier material rises to as much as $8 per cent. (at Milverton). 
