The Scottish Naturalist. 



155 



particles and their conveyance by rivers and streams, tell us how- 

 sand has been deposited on sea-beaches and accumulated in sand- 

 banks ; but we have still to search for the origin of these minute 

 particles which chiefly compose sand. I refer to the typical 

 element of it, viz., quartz or silica. It is a remarkable feature in 

 the sand of the Fife coast that quartz is the principal ingredient, 

 and the trap rocks, the most common in the district, are re- 

 presented only to a very insignificant extent. 



In granite we can trace the presence of the elements of sand. 

 As already remarked, granite is composed of quartz, felspar and 

 mica or hornblende. Now the quartz grains in granite are 

 identical with those we find in sand. On comparing the sand of 

 Brodick Bay, Island of Arran, with the decomposing granite I 

 found at the top of Goatfell, there is a striking resemblance. The 

 quartz crystals in the granite are mostly broken, but in many 

 instances the perfectly formed crystals can be observed • their 

 angles and planes being distinctly seen after rubbing down some 

 of the weather-worn portions of this granite. Sand is found ready- 

 made, but not rounded nor water-worn after the manner of sand 

 on the sea-beach, and of that composing sandstones. The sand from 

 Brodick Bay consists mainly of quartz crystals. That manu- 

 factured from the granite of Goatfell is mostly composed of felspar 

 — the principal mineral element of granite. 



This leads now to the question how is this hard granite rock 

 disintegrated and reduced to grains of sand ? It is by exposure 

 to the atmosphere, chiefly by the action of the carbonic acid gas. 

 Felspar (composed of a silicate of sodium or potassium) forming 

 the main bulk of granite, carbonic acid has a decided affinity to 

 the soda, and in a greater degree to the potash in it. It seizes, or 

 unites with, whichever is present ; and the result is the formation 

 of carbonate of soda or of carbonate of potash. The silica and 

 alumina present, in nearly equal parts (with 15% of water), remain 

 in the form of kaolin or china clay. In Cornwall the deposit of 

 kaolin clay is found in the valleys, while the hills or ridges are 

 composed of granite. 



Roughly estimated, there is about one ton of sand to 7 tons of 

 clay, while about one-third of the sand is mica. Dr. Sorby, in 

 his examination of sand in the south of England, found it in 

 Devonshire to consist mainly of angular grains of quartz, 

 only about one-tenth part of which were worn. Passing to the 



