102 The Ottawa Naturalist. 



frequently changed to hard quartzites, shales to cleaved slates, and 

 limestones to a crystalline condition, as marbles. Often all the altera 

 tion is directly due to the presence of heated masses of intrusive rock, 

 as granite, syenite or diorite, which have ascended from the heated 

 interior along lines of fracture or least resistance, and the heat has 

 depiived the rock in contact of much of the contained moisture, 

 changing the texture and altering its character for a considerable 

 distance from the line of contact of the intrusive mass. 



As regards some of the more important minerals found in the 

 stratified rock, their formation has proceeded on somewhat similar lines. 

 Tnus if we study the early history of the coal beds, some of which have 

 a thickness of from thirty to forty feet, we find that they have originated 

 probably from swampy deposits somewhat of the nature of our present 

 peat mosses, and that the growth and decay of vegetable matter went 

 on for very long periods. On the basis of eight to ten feet of peat or 

 swamp mud being required for every foot of coal produced, a thirty 

 foot coal seam would have requited a swamp of enormous depth to 

 have furnished the material necessary for the formation of such a coal 

 bed. That the coaly matter has been derived from the decomposition 

 of plants, such as tree ferns and other allied forms, which grew in the 

 marshes of the Carboniferous time is very clear, since the remains of 

 the coal-plants can be found well preserved in the shales which overlie 

 the coals ard in the clays which form their underlying strata, as well as 

 in the tissue of the coal itself. It would appear that the woody or 

 interior tissue gradually became destroyed, while the carbon of the 

 bark principally formed the mass of the coal itself. These masses of 

 swamp or peaty matter, gradually by submergence become overspread 

 with sand, gravel or silt, which by continued increase in thickness 

 acquired sufficient weight to pre-s down the miss of bog, until by long 

 continued pressuie and other causes it became transformed into the 

 coal which we mine and burn to-day. 



Somewhat similar changes and conditions are going on at many 

 places at the present time in our own peat deposits. Thus at the great 

 bog near the city known as the " Mer bleu " which is a great expanse 

 of peat of from 8 10,000 acres in extent, the surface is covered with 



