122 T. Crook Sf G. M. Davies — Si. Ives Ba// Sand, Cornicall. 



The tourmalines are chiefly brown ; but some are blue, while others 

 are almost colourless in ordinary light. 



The impure and weakly magnetic quartz is in part rusty and in 

 part impregnated with fine needles of tourmaline. The non-magnetic 

 quartz is very dusty in appearance, due to the abundance of liquid 

 inclusions, "with numerous gas bubbles. 



■ The non-magnetic portion heavier than bromoform consists almost 

 wholly of fluorspar, with only small amounts of the other constituents, 

 including andalusite, topaz, killas fragments impregnated with tinstone 

 granules, and a few small free grains of tinstone. 



The fluorspar fragments are mainly colourless, but many of them 

 show a well-marked violet colour. They are isotropic. They exhibit 

 the characteristic octahedral cleavage, yielding numerous triangular 

 plates with bevelled edges. Their very low refractive index is 

 a striking feature. 



The andalusite fragments are partly irregular in shape, but some of 

 them are elongated prisms, with definite limiting edges ; these latter 

 show straight extinction. They have a refractive index about 1"64, 

 and are optically negative. They exhibit the characteristic pleochroism, 

 showing the rose tint when the short diagonal of the polarizer is along 

 the length. 



The topaz fragments are partly granular and partly in the form of 

 good basal cleavage plates. These latter show the normal emergence 

 of the acute bisectrix, which is positive; and they also show the feeble 

 birefringence characteristic of basal flakes of topaz, with a refractive 

 index near 1-61. 



Siderite in rhombohedral cleavage plates, pale spinel in irregular 

 grains or octahedra, zircon crystals, ilmenite, epidote, muscovite, free 

 grains of tinstone, and probably also rutile and blue corundum are 

 seen occasionally in the sand. 



A lighter-coloured sand from near low-water mark at the same 

 locality, and another from near Lelant about half a mile to the west 

 of Hayle Elver, both contained about 70 per cent, of shell fragments, 

 etc. Their insoluble residues contained the same ingredients as the 

 specimen already described, but in different proportions ; and the 

 heavier minerals -were present only in small amounts. 



It seems, therefore, that fluorspar, andalusite, topaz, and tinstone 

 are probably distributed throughout the sands of St. Ives Bay. The 

 amount of fluorspar is considerable, that of andalusite and topaz 

 small, whereas the amount of tinstone is very small, the mineral being 

 mostly present as fine granules disseminated in killas fragments. 

 The presence of these minerals is not surprising, considering their 

 abundance in the granite and killas of Cornwall ; but it is perhaps 

 rather remarkable that one can pick up sands so rich in fluorspar. 



There can be little doubt that the non-calcareous portion of these 

 sands consists chiefly of the products of mining activity brought 

 down to the coast by the Red River. It appears to be practically 

 identical in its general character with the Red River sand described 

 by the ofiicers of the Geological Survev (see Memoirs, "Geology 

 of Falmouth and Camborne," 1906, p. 273). The total amount of 

 stamp-battery products and other mining refuse brought down by the 



