How Rocks are Formed. 163 



green moss, ferns, shrubs and stunted trees, the whole forming a light 

 colored layer of two or three feet in thickness. Beneath this the 

 contents of the bog gradually become dense and darker colored ; the 

 green living vegetation has disappeared, but its remains yet exist in the 

 form of rootlets, stems &c. Still lower down the bog presents a still more 

 homogenous aspect, the vegetable matter is almost entirely decomposed, 

 and the mass is of a uniform dark brown or black color and of a very 

 considerable density, forming a very excellent fuel when dug out and 

 dried. Where this material is subjected to great pressure it furnishes a 

 material known as compressed peat which can be' so manufactured as 

 to have all the density and calorific power of coal itself, and thus is able 

 to furnish a material of very great value for all the purposes for which 

 ordinary coal is now applied. There is therefore a manifest resemblance 

 between these modern bogs and those from which our beds of mineral 

 fuel were derived ; with this exception, that the character of the growing; 

 vegetation, and the nature of the animal life which inhabited these were 

 widely different; while the presumption is strong that if these peat bogs 

 could be subjected to the same conditions which affected those of the 

 Carboniferous time, the resulting material would be a coal of somewhat 

 similar character. Coals of an intermediate character are also found as 

 in the great lignite deposits of the Saskatchewan and Souris areas, where 

 the mineral still retains to a marked extent its original woody fibre. On 

 the other hand when the bituminous coals have been subjected to the 

 action of further heat and pressure, the result appears in the form of 

 authracite or hard coal, in which much of the volatile matter has been 

 driven off. A still further alteration results in the formation of 

 graphite. Beautiful illustrations of this latter condition are found in 

 some deposits in southern New Brunswick, where the coal is graphicized 

 anthracite, the containing rocks being thrown on edge and much 

 altered. 



Other kinds of rock masses may be mentioned, such as rock-salt, 

 gypsum, shell-marl, infusorial earth, chalk, iron ores of various kinds, 

 petroleum and petroleum-bearing shales. Of these, rock-salt has 

 probably been formed by the evaporation of saline waters in enclosed 

 basins, a process which has been going forward at many stages of the 



