368 ROCK*. 



lower level for withdrawing the lime. The lime is taken 

 out below and the stone thrown in above, and this may be 

 kept up without intermission as long as the kiln lasts. Be- 

 neath the furnaces there are also ash pits. Such a kiln is 

 most convenient for being filled and emptied when situated 

 on a side hill. 



The localities of limestone in the United States are too 

 common to need enumeration. Hydraulic limestone is also 

 abundant. 



Quicklime is much used for improving lands; also for 

 clarifying the juice of the sugar cane and beet root ; for puri 

 fying coal gas ; for clearing hides of their hair in tanneries 

 and for various other purposes. 



SAND. CLAY. 



The loose or soft material of the surface of the earth con- 

 sists of sand, clay, gravel or stones, and what we call in general 

 terms, soil or earth. These materials are either in layers 

 or irregular beds. Most clay beds, and many of gravel, 

 when cut through vertically, show indications of horizontal 

 layers, a result of deposition, or distribution, by water. 



The ordinary constituents of earth are quartz, feldspar or 

 clay, oxyd of iron and lime ; but these vary with the source 

 from whence they are derived When the rock that has 

 afforded the soil is granite, mica slate, or the allied rocks, 

 mica is usually present, as well as feldspar and quartz ; so 

 a quartzose rock will furnish siliceous gravel ; a magnesian, 

 will give magnesia to the soil ; calcareous, lime ; trap, the 

 ingredients of decomposed feldspar or hornblende. The 

 material will be coarse or gravelly, or fine earthy, according 

 to the nature of the rock, or the condition under which it is 

 worn down, or its subsequent distribution by flowing waters. 

 Besides the prominent constituents mentioned, there are 

 small proportions of phosphates, nitrates, chlorids, etc., toge- 

 ther with the results of vegetable decomposition ; and these 

 comparatively rare ingredients are of great importance to 

 growing vegetation. The pebbles of a soil are commonly 

 siliceous, as this kind resists wear most effectually. 



Sand is usually pulverized quartz, often with some feldspar. 

 Clay is a plastic earth, consisting mainly of pulverized or 

 altered aluminous minerals (largely feldspar) and quartz, the 

 latter about two-thirds the whole. The alumina is often 



