Vol. 58. ] CONSTITUTION OF THE BUNTER PEBBLE-BED. 621 
The following is the percentage of material of specific gravity 
greater than 2°58, at various localities along the outcrop of the 
Pebble-Bed, taken from south to north :— 
Per cent. 
Budleich Saltontonmeneeste creel seen. 75 
Fair Mile, near Tallaton............... 79 
Wtkeulias ; | ce ORO ee ees Wee og 71 
ipurlescombes4 25 ese ee ae 78 
MSL VOrEO na. : fsteeeec ee aoe seen 83 
Bitzheagd’ 2.4 ho eee een aee anes Ree ce 83 
It is interesting to note that the percentage of heavy material 
and the percentage of light material are almost constant throughout 
the thickness of the bed at Budleigh Salterton, being 75 and 25 
respectively. This, unfortunately, was the only locality where 
there was a section from which I could be sure of collecting a 
series of samples at regular intervals, from the top to the bottom of 
the deposit. Rounding of the grains has taken place, but the 
degree of rounding is by no means constant, even in the same 
sample. However, taking into consideration any one 
mineral, we notice that the rounding becomes more 
complete as we travel from south to north. 
The chief mineral species that occur in the sands forming the 
- matrix of the Pebble-Bed, arranged according to their crystal- 
systems, are :— 
Cubic. Tetragonal. 
Fluorspar. Anatase. 
Garnet. Cassiterite. 
Magnetite. Rutile. 
Zircon. 
Rhombohedral. 
Apatite. Orthorhombic. 
Ilmenite. Brookite. 
Tourmaline. Sillimanite. 
Quartz. Staurolite. 
Monochimie. Triclinic. 
Biotite. Cyanite (disthene). 
Muscovite. Microcline. 
Orthoclase. 
Sphene (titanite). 
Under the head of amorphous minerals and compound grains 
may be mentioned :— 
Felsite, quartzite, and chert. 
Shimmer-aggregates, pinite, and mica-schist. 
Leucoxene, and other decomposition-products. 
The following comprises a description of the species and grains 
mentioned above, giving in some instances the chief characters by 
which the minerals were identified. 
Fluorspar.—this mineral occurs in colourless isotropic grains, 
usually angular, with the octahedral cleavage {111} well shown. 
They reach a size of 0°40 millimetre in greatest length. The index 
