KINDS OF SOILS. 153 



WO may infer tliat lime is abundant in tlie soil. On the 

 other hand, if a soil contains a large pioportion of quartz 

 pebbles, the leuitimate inference is that it is of compara- 

 tively poor quality. The term gravelly admits of various 

 qualification. We may have a very gravelly or a mod- 

 erately gravelly soil, and the coarse material may be char- 

 acterized as a fine or coarse gravel, a slaty gravel, a 

 granitic gravel, or a diorite gravel, according to its state 

 of division or the character of the rock from which it was 

 formed. 



But the closest description that can thus be given of a 

 gravelly soil cannot convey a very precise notion of even 

 its external qualities, much less of those pro})erties upon 

 which its fertility depends. 



Sandy Soils are those which visibly consist to a large 

 degree, 9U° |^ or more, of sand, i. e., of small granular 

 fragments of rock, no matter of what kind. Sand usually 

 signifies grains of quartz', this mineral, from its hardness, 

 withstanding the action of disintegrating agencies beyond 

 any other. Considerable tracts of nearly pure and white 

 quartz sand are not uncommon, and are characterized by 

 obdurate barrenness. But in general, sandy soils are by no 

 means free from other silicious minerals, especially feldspar 

 and mica. When the sand is yellow or red in color, this fact 

 is due to admixture of oxide or silicates of iron, and pohits 

 with certainty to the presence of ferruginous minerals or 

 their decomposition-products, which often give considera- 

 ble fertility to the soil. 



Other varieties of sand are not uncommon. In New 

 Jersey occur extensive deposits of so-called green sand, 

 containing grains of a mineral, glauconlte, to be hereafter 

 noticed as a fertilizer. Lime sand, consisting of grains 

 of carbonate of lime, is of frequent occurrence on the 

 shores of coral islands or reefs. The term sandy-soil is 

 obviously very indefinite, including nearly the extremes 

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