MARL. • 83 



MARL. 



Description. This substance is arranged by Cleaveland as a sub-species of carbonate of 

 lime, of which indeed it is essentially composed. Some marls are more or less indurated, 

 while others are frijible and earthy. In some the argillaceous ingredient is comparatively 

 small ; in others, again, it abounds, and furnishes the predominant characters. The calcareous 

 and argillaceous marls unite by imperceptible degrees, and the latter sometimes pass into 

 clay. Marls, therefore, are sometimes arranged under,the heads of calcareous and argillaceous, 

 and sometimes under those of the indurated and the earthy. 



The term fresh water marl is applied to those accumulations which have been formed by 

 the decay of successive generations of shells at the bottoms of lakes or ponds. In marshes 

 that were once ponds, the marl is often covered by a deposit of peat, arising from the growth 

 and decay of plants. 



The marls usually disintegrate or crumble by exposure to the atmosphere for a longer or 

 shorter period, depending upon their nature. The same changes generally take place in a 

 very short time when marl is immersed in water, with which it forms a short paste. It is 

 probably to these properties that this substance owes its value as a manure. 



Composition. All marls effervesce with acids, sometimes very briskly and sometimes 

 feebly, according to their solidity and the proportion of carbonate of lime, which may vary 

 from twenty-five to eighty per cent. ; indeed in the argillaceous marls it is often much less.* 



To ascertain the proportions of the ingredients of a marl, a known weight of it may be 

 treated with dilute muriatic acid, by which the calcareous part will be dissolved ; and the 

 residue, Ijeing dried and weighed, will give the amount of clay with sufficient accuracy to lead 

 to correct conclusions in regard to its use as a fertilizing agent. t 



There are in this State many rich and extensive localities of marl, but their value does not 

 appear to be appreciated. The following are more particularly deserving of notice. 



Alb.\ny County. In the towns of Bethlehem and Coeymans in this county, there are 

 beds of marl of some extent, which contain from forty to eighty-five per cent, of carbonate of 

 lime. They have not, however, it is believed, been much used for agricultural purposes. 



Cayuga County'. According to Mr. Hall, the Cayuga marshes, which embrace an area of 

 forty thousand acres, are in many, and probably in all places, underlaid by marl to the depth 



* Cleaveland. Elementary Trr^atise on Mineralogy and Geology. 



t According to Chaptal, "Marl is principally composed of sub-carbonate of lime and alumina; iho proportions ni which these 

 are combined constitute all its varieties. The lime contained in marl, as it is taken from the bed, is neversaturatej with carlionic 

 acid ; but after being exposed to the air, it becomes at length saturated with the acid it receives from it, cmmbles and eflloresces. 

 The decomposition of marl may be hastened by frequently turning it, so as to allow the air free access to the lime ; and thi.s me- 

 thod is generally practised by those who employ marl as a manure." Chemistry applied to Agriculture. Amer. Ed. p. 44. 



