628 MINERALS OF THE BUNTER PEBBLE-BED. _[ Nov. 1902. 
IIT. Posstsre Directions of THE SEDIMENT-BEARING CURRENTS, 
AND SouRCES oF THE Mrnerat-Grains, 
There are many peculiarities in the distribution of the foregoing 
minerals, which point more or less distinctly to the direction in which 
the material was carried. From these we may, I think, deduce the 
existence of a southerly main current, over the whole line from 
the southern coast of Devon to Fitzhead in Somerset, a distance of 
about 30 miles; and at the same time it will be seen that this 
main current was joined to the north of Uffculm by a minor current, 
probably from the west. 
The evidence for the foregoing statement is as follows :—Taking 
into consideration the percentage of material with a specific gravity 
greater than 2°58 (see p. 621), we see that from 75 per cent. at 
Budleigh-Salterton it falls gradually northward until at Uffeulm 
(20 miles to the north) the percentage is 71. It now begins to rise, 
and continues to do so until it reaches as much as 88 per cent. in 
the neighbourhood of Milverton in Somerset, north of which the 
percentage again falls. The gradual diminution of the percentage 
of heavier material as we pass from south to north, would in itself 
suggest a transport of material in that direction; while the rise in 
the neighbourhood of Burlescombe would point to a fresh influx of 
material. This view is strengthened by the distribution of the 
individual minerals. For instance, staurolite, which is so plentiful 
in the extreme south, diminishes considerably in quantity in the 
more northerly part of the outcrop of the Pebble-Bed, and a gradual 
diminution in the size of the rounded tourmaline-grains has been 
noted in the same direction. Fluorspar does not extend north- 
ward farther than about + or 5 miles from the coast. Associated 
with the rise in percentage of the heavy material at Burlescombe 
and: the other localities near, an assemblage of minerals occurs which 
differs markedly from that of the normal, more southerly type. 
Several minerals, such as garnet and cassiterite, make their 
appearance for the first time, and the blue variety of tourmaline 
becomes more common. It thus seems probable that the main 
current was from the south, which is in accordance with the 
conclusion arrived at by Mr. Ussher’ from a study of the distribution 
of the pebbles. 
The confluent westerly current is simply one of many minor 
currents such as are met with in any drainage-system. 
When we consider what are the minerals which have been 
recorded, we can hardly refrain from concluding that an area 
differing widely from any in the South or West of England must 
have been undergoing denudation to supply them. The occurrence 
of minerals such as staurolite, cyanite, sillimanite, microcline, and 
probably cordierite, and the prevalence of ‘shimmer-aggregates,’ 
suggest some great metamorphic area as the source of much of the 
material. So far as is known at present, staurolite does not occur in 
the metamorphic rocks round the Devon-Cornwall” granite-masses, 
1 Mem. Geol. Surv. ‘ Exeter’ 1902 (in the press). See also W. A. E. Ussher, 
Quart. Journ. Geol. Soc. vol. xxxiv (1878) pp. 246-47. i 
* K. Busz, Neues Jahrb. Beilage-Band xiii (1899) p. 90. 
