154 ON THE RATIONALE OF CERTxVIN MANURES 



day, wlio, in order to prevent the alkaline ing-redients of his 

 manure from being* carried off before the cro}) has had time 

 to take them up, combines them with carbonate of lime, 

 and thus produces a more sparing-ly soluble combination. 



Let us, indeed, for a moment stop to consider what would 

 have been the consecjuence had this natural provision for 

 economizing- the resources of the soil been omitted ; one of 

 the most formidable of which would have been that, before 

 the present stage of the world's existence, all the alkalies 

 existing- in the superficial strata of the earth must have 

 found their way into the ocean, when, even supposing- their 

 presence in such excess had not proved destructive to the 

 marine plants which take them up — supposing- even their 

 abundance to have stimulated the marine veg-etation, and 

 thus to have afforded an exuberant g-rowth of alg-fie adapted 

 for manuring- the tracts of land that lie contig'uous to the sea 

 — still the inland portions of our continents must have 

 remained absolutely ban-en, from the impossibility of trans- 

 porting-, to any great distances from the coast, the produce 

 of the sea, which, in the case supposed, could alone have 

 returned to the land those soluble ingredients which the 

 rains of preceding- ages had carried away. These conse- 

 quences are prevented by the state of combination in which 

 the alkalies naturally exist in the soil, as they are thus 

 brought into solution so sparing-ly, that the whole, or nearly 

 the whole of them present in the water which the soil retains, 

 is taken up by plants ; whilst the latter, as they decay, render 

 these principles back again to the soil, in a more available 

 condition, indeed, but still in one which o]iposes some im- 

 pediments to their being carried of speedily by water. 



Hence the vast accumulation of alkalies locked up within 

 the forests of most thinly peopled countries ; hence the un- 

 rivalled fertility of virgin soil, enriched by the annual tri- 

 bute paid to it by these forests at the period of the fall of 

 the leaf — hence, too, the miasmata so apt to occur in new 

 countries thus circumstanced, whenever the soil is disturbed 

 by the processes of agriculture, and the decay of the vege- 

 table debris accelerated by the free introduction of air and 

 moisture. 



I may here just allude to another interesting- provision, by 

 which the slow but continuous disengagement of alkalies 

 from certain rocks of igneous origin seems to be secured. 



I allude to the fact, that, whilst igneous rocks which have 

 cooled rapidly appear to be in the condition of glass — that 



