394 THE CANADIAN NATURALIST. [Dec. 



state of refrigeration this process is so slow that the increase of 

 temperature in descending is only about one degree centigrade 

 for each hundred feet ; but if we admit the hypothesis of a cooling 

 globe, it can be shown that in early geologic ages this increase 

 must have been tenfold, or even twenty-fold greater than at 

 present. As this augmentation of temperature in depth obeys the 

 same law alike in the newest and the oldest formations, it follows 

 that the accumulation of sediment at any time and place will 

 result in a slow rise in temperature of the portion covered thereby, 

 so that a deposit of a few miles in thickness in comparatively 

 recent ages, and probably one of as many thousands of feet in the 

 Laurentian or even the paleozoic period, would, after a lapse of 

 time, so elevate the temperature of the buried portions as to 

 produce new chemical and mechanical arrangements of the sedi- 

 ments. The expansive action of heat upon these porous materials, 

 which generally include several hundredths of water, would soon 

 be counteracted by the great contraction following chemical 

 combination, resulting in the formation of new and denser 

 compounds, which constitute the crystalline and metamorphic 

 rocks. The action of silicious matters in the presence of water, 

 aided by heat, upon the various carbonates, chlorides, sulphates, 

 and organic matters which abound in most sedimentary forma- 

 tions, would generate the acid gases which are so often evolved in 

 volcanic eruptions. It must be borne in mind that water under 

 pressure, and at high temperatures, develops extraordinary solvent 

 powers ; while from what has already been said of the influence 

 of pressure in favoring solution, it will be seen that the weight of 

 the overlying mass becomes an efficient cause of the liquefaction 

 of the lower portions of the sedimentary material. Time is 

 wanting to discuss the great forces which from early geologic 

 periods have been active in transferring sediments, alternately 

 wasting and building up continents. By the depression of the 

 yielding crust beneath regions of great accumulation there follows 

 a softening of the lower and of the more fusible strata, while the 

 great mass of more silicious rocks becomes cemented into 

 comparative rigidity, and finally, as the result of the earth's 

 contraction, rises a hardened and corrugated mass, from whose 

 irreo-ular erosion results a mountainous region. 



Those strata, which from their composition yield under these 

 conditions the most liquid products, are, it is conceived, the 

 source of all plutonic and volcanic rocks. Accompanied by water, 



