346 THE BEGOLITH 



quenee of soil formation through the breaking down of rocks 

 by the processes of weathering, whereby all but the most in- 

 destructible portions are lost. 



The predominantly inorganic nature of any soil may easily 

 be shown by fractional separations, made either by washing, 

 or by sieves of varying degrees of fineness, whereby it is 

 brought into portions of like size and weight such as can con- 

 veniently be submitted to microscopical and chemical analyses. 

 All portions, from the finest dust to particles of such size as to 

 be classed as pebbles, will thus be found to be but mineral 

 matter, particles of quartz, feldspar, shreds of mica, and other 

 silicates in ever-varying proportions and stages of alteration 

 or decomposition. 



Owing to the destructive nature of their formation, it is but 

 natural that a soil, particularly one of considerable antiquity, 

 should but slightly resemble the parent rock. This fact was 

 more than suggested in the chapter on rock-weathering. In 

 order that its significance may be fully comprehended, the 

 analyses of fresh rock and corresponding residual material from 

 various sources are given in the table on the next page. 



The most striking of the dissimilarities shown by this table 

 are, as is to be expected, those of the limestone soils, in columns 

 I and II, where the proportional amounts of silica, iron and 

 alumina are increased, roughly speaking, nearly one hundred 

 fold, while the amount of lime carbonate is correspondingly 

 diminished. This condition of affairs is still further exag- 

 gerated in the case of the red soil of Bermuda (columns III and 

 IV) which offers particularly favorable opportunities for study, 

 owing to the isolated condition of the islands and the consequent 

 freedom from danger of contamination by other than local drift. 



The shells and corals which in a more or less consolidated con- 

 dition form the entire mass of these islands, although essentially 

 of carbonate of lime, are nevertheless not entirely so, carrying, 

 aside from the magnesia, about 1% of inorganic impurities, 

 chiefly oxides of iron and alumina and earthy phosphates, which 

 are practically insoluble in the water of rainfalls, with which 

 alone we have to do here. As time goes on, the lime is slowly 

 leached out and carried away into the ocean, the insoluble parts 

 remaining. Throughout the centuries of decay, this 1% of 

 insoluble impurities, representing but one ton of residue to 

 every 99 tons removed, slowly accumulates until it forms the 



