T. Crook 8f G. M. Davies — St. Iven Bay Sand, CornuaU. 121 



fragments to the heavier and more granular ingredients of the sand 

 varies considerably, especially within the limits of high- and low- 

 water marks, as is usually the case. Some of the heavier ingredients 

 are dark-coloured, and may be observed to have been streaked out in 

 bands or aggregated in patches at the surface, where they have been 

 concentrated by the action of the waves. Where heavy minerals 

 abound, tidal action can be seen to have effected a persistent concen- 

 tration about the mean high-water mark, where the heavier ingredients 

 predominate for at least a foot beneath the surface. Such a band 

 can be easily traced for a considerable distance in the vicinity of the 

 Eed River. 



A specimen collected from this band at a point about midway 

 between Red River and Hayle River was found to contain about 

 30 per cent, of shelly matter, etc. The residue left after dissolving 

 this calcareous portion of the sand in cold, weak acid was found 

 to have approximately the following mineral composition : — 



Strongly 



maffnetic 



Weakly 



raaijiietic 



Non-maarnetic 



Magnetic iron oxide 



Killas fragments 

 Tourmaline 

 Impure quartz 

 Brown biotite 

 Chlorite 

 Siderite 



Quartz 

 Felspar 

 Killas fragments 



Fluorspar 

 Andalusite 



Topaz 



Free tinstone 



Killas fragments im- 

 pregnated with tin- 

 stone 



Zircon 



Spinel 



Per cent. 

 1 



Y 74 



Dark- 

 coloured 

 portion. 



l<2-84 ' 



J (bromoform) I 



10 



> 2-84 

 < 3-32 



s.g. 



> 3-32 

 r (methylene 

 I iodide) 



15 



(almost 



wholly 



fluorspar) 



Light- 



coloured 



portion. 



The constituent referred to as magnetic iron oxide is complex. It 

 appears to be partially hydrated, and probably consists of a mixture 

 of magnetite, hoematite, and hydrated iron oxide, the magnetite 

 predominating. With the exception of a slight amount of haematite, 

 it is opaque even in the smallest particles. It is apparently non- 

 titaniferous. 



The killas fragments show a very compact structure ; they are for 

 the most part weakly magnetic, owing to the presence of magnetic 

 enclosures, many of which are black, and consist, in part at least, of 

 magnetic iron oxide. The non-magnetic killas fragments are either 

 free from dark enclosures or are impregnated with granules of tinstone ; 

 in the former case they float in bromoform, in the latter they may 

 sink even in methylene iodide. 



