THE NONMETALLIC MINERALS. 477 



than 0.25mm. in diameter, interspersed with finely pulverulent matter 

 which can only be designated as clay. The yellow-brown color of the 

 sand is due to the thin film of iron oxide which coats the larger gran- 

 ules. When this film is removed by treatment with dilute hydrochloric 

 acid, the constituent minerals are readily recognized as consisting mainly 

 of quartz and feldspar fragments (both orthoclase and a plagioclase 

 variety), occasional granules of magnetic iron oxide, and irregularly 

 outlined scales of kaolin, together with dust-like material too finely 

 comminuted for accurate determination. . Many of the larger granules 

 are white and opaque, being presumably feldspar in transition stages 

 toward kaolin. An occasional flake of hornblende is present. The 

 term greensand 1 is applied to the argillaceous molding sands, in an 

 undried state, and which is employed in its native state, new and damp. 

 The term dry mnd is used in contradistinction, to indicate a sand that 

 must be dried by heat before being fit for use. The dry sand is stated 

 to be firmer and better adapted than the green for molding pipes, col- 

 umns, shafts, and other long bodies of cylindrical form. 



In England good molding sands are obtained from the Lower Mot- 

 tled Sands of the Bunter (Trias) beds and from those of the Thanet 

 (Lower Eocene). 



6. MINERAL WATERS. 



From a strictly scientific standpoint any water is :i mineral water, 

 since water is itself a mineral an oxide of hydrogen. Common usage 

 has, however, tended toward the restriction of the name to .such 

 waters as carry in solution an appreciable quantity of other mineral 

 matter, although the actual amounts may be extremely variable. 



Of the various salts held in solution, those of sodium, calcium, and 

 iron are the more common, and more rarely, or at least in smaller 

 amounts, occur those of potassium, lithium, magnesium, strontium, 

 silicon, etc. The most common of the acids is carbonic, and the next 

 probably sulphuric. 



Classification. The classification of mineral water is a matter at- 

 tended with great difficulty from whatever standpoint it is approached. 

 Such classification may be either geographic, geologic, therapeutic, or 

 chemical, though the first two are naturally of little value, and the 

 therapeutic, with our present knowledge, is a practical impossibility. 

 The chemical classification is, on the whole, preferable, although even 

 this, owing to the great variation of methods of stating results used 

 by analytical chemists, is at present attended with some difficulty. 

 Dr. A. C. Peale, the well-known authority on American mineral 

 waters, has suggested the scheme given below, 2 and from his writings 

 has been gleaned a majority of the facts here given. 



1 This must not be confounded with the Greensand marl, or Glauconitic sand used 

 for fertilizing purposes, and mentioned on page 369. 



2 Annual Report of the U. S. Geological Survey, 1892-93, p. 64. 



