96 ECONOMICAL MINERALOGY. 



It has been supposed by some that peat is constantly renewed ; by others, this has been 

 doubted. It is evidently the result of some change in the layers of vegetables deposited after 

 their death, at the bottom of marshes or lakes, where they are mixed with mud and the re- 

 mains of aquatic plants. But the fact that peat is not found in all marshes, leads us to sup- 

 pose that its formation is due to some peculiarity in the vegetables, or in the circumstances 

 attending their decomposition. Hence the opinion which has been entertained, that peat has 

 been formed under conditions which do not now exist. 



Peat is employed as a combustible in many parts of Europe. In Great Britain, its use as 

 an economical fuel is very general where it abounds, but more particularly in Scotland and 

 Ireland ; one tenth of the latter being supposed to be covered with bog matter. Where it 

 exists plentifully in England, it is sometimes burnt, either in admixture with coal itself, or as 

 a cheaper substitute ; and it is even stated, that so far is it from being altogether excluded in 

 those counties most noted for coal, that even in Northumberland, as well as Yorkshire, con- 

 siderable quantities of peat firing are expended.* Its combustion is with some difficulty com- 

 menced, but it afterwards burns steadily with the evolution of fiame. The disagreeable odour 

 which it gives out is an objection to its use in domestic economy, but this does not apply to 

 its employment in many of the arts. It seems to be admitted, that of all combustibles, peat 

 is that which gives out the most equable and constant degree of heat. 



We are informed by Beckman, in his History of Inventions, that in some parts of Bohemia, 

 Silesia, Upper Saxony and other places, it is common to subject the turf used in working 

 pietals, to a certain degree of combustion in kilns or furnaces. After undergoing this process, 

 it is supposed to kindle sooner, bum with less air, and to form a more moderate and stiU more 

 uniform fire than when the article has not been thus prepared. Charred peat is also used by 

 the smiths in some parts of Great Britain, in tempering edge tools. The process of carboniza- 

 tion removes many of the objections to the employment of peat. 



GRAPHITE OR PLUMBAGO. 



This substance, which is also often known by the name of Black Lead, may be ranked 

 among the useful minerals. 



Description. Graphite has a dark steel-grey colour, a metallic lustre, and a splendent and 

 metallic streak. 



Hardness 1 ; for it is easily scratched by gypsum, but scarcely by talc. It is sectile, has 

 a greasy feel, and writes readily on paper. Thin laminae are highly flexible. Opaque. 



Specific gravity from 2.08 to 2.45 :(5eM(^a«(). ... ... „, • 



sure to the air, it stiffens and consolidates : it is then cut and cross-cut with the spade into cubic masses, which, on becoming 

 dry, are found to burn with great freedom, in consequence of the bituminous saturation, to which the matterof ihem seems to have 

 been subjected." History and DescriptUn of Fossil Fuel, the Collieries, and Coal Trade of Great Britain. Lond. 1835. 

 * History and Description of Fossil Puelf the Collieries^ and Coal Trade of Great Britain. Lond. 1835. 



