ON MANURES. 107 



this summary description, its appearance is, however, as 

 varied as its properties, being of colour nearly pure white, to 

 the darkest shades of brown and red, interveined with blue 

 and yellow. It also exists in different kinds of land, is seldom 

 found as a stratum of much length, but generally in detached 

 masses at various depths, sometimes in wide and dense per- 

 pendicular layers, at others in streaks, running in lines pa- 

 rallel with the horizon, or again intersecting each other at 

 right angles, usually resting on sand or gravel, and is classed, 

 according to its qualities, into the following distinct species: 



1. Clayey marl, which improves sandy land, and seems to act 

 as clay in changing the nature of the soil. In land consisting 

 of a mixture of sand and loam, or of sand and gravel, then, the 

 application of this marl has been found peculiarly advanta- 

 geous: and on all poor and thin sandy soils there is this 

 further advantage in its use — that, from the large proportion 

 of clay which it usually contains, it adds to their bulk and 

 firmness, and thus has a tendency to bring them to that 

 medium state which is the most favourable to the purposes of 

 vegetation. It is more soft and unctuous than clay; indeed, 

 upon slightly cutting it, it becomes so flexible, that it may 

 be kneaded like dough, or paste, though, when the moisture 

 evaporates, it falls into pieces: it therefore blends easily with 

 the soil, and partaking more largely of calcareous matter, 

 its effects, though slow, are in all the latter cases more 

 fertilizing. 



2. Sandy marl, which is far more frequent in Ireland than 

 in any part of England, and is commonly found in pits of lime- 

 stone-gravel, whence it is in that country usually called lime- 

 stone-sand. It is seldom clammy or unctuous, like the clay 

 marl, nor does it adhere to the tongue, but crumbles between 

 the fingers, and feels gritty; when exposed to the air and 

 moisture, it slowly chips and moulders; and it partakes of 

 some extraneous mixtures. Its colour is sometimes like that 

 of lead, or brown, approaching to black, and at others blue. 

 As implied by its name, it contains an excess of sand over that 

 of clay ; for, upon analyzing it, the proportion of the former 

 has, in most cases, been found to be from 60 to 80 per cent. ; 

 and it does not effervesce with acids so quickly as the calca- 

 reous marls. It possesses but a small degree of tenacity, and 



as a manure, makes no ebullition with acids ; neither do several of the red 

 marls; yet many of Ihem are known to be productive of great improvement 

 to land. 



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