302 Researches in the Theory and Calculus of Operations. 



to allow tne calm process of crystallization to occur (the 

 lower crystallines); soon, however, to be covered by fresh 

 deposits of more heterogeneous composition, the heavy 

 and increasing pressure of which, conjoined with the action 

 of the central heat, converted the underlying formation into 

 the so-called metamorphic strata; while fresh arrivals, find- 

 ing less intensity of heat, usher in successively the siliceous 

 and argillaceous strata constituting the laurentian, Cam- 

 brian, and silurian series, in some members of which the 

 earliest traces of organic existence are found, increasing in 

 numbers in ascending direction. Then entered the Coal 

 era, when the subsiding thick carbonaceous vapor, uniting 

 with the ever-present oxygen, stimulated the growth of im- 

 mense fields or swamps of acrogenous vegetation, first 

 spreading and partially floating out over large areas of 

 oceanic waters, subsequently subsiding by their own in- 

 creasing weight, afterwards buried under accumulating 

 masses of siliceous, calcareous, etc. deposits, under the 

 pressure of which, conjoined with the permeating central 

 heat, this mass of vegetable matter was converted into 

 beds of coal, much of which we now exhume and feed to 

 the iron horse, etc. As restless time strode on its ceaseless 

 course, the neptunian forces (rains and rivers) pursued their 

 warfare against the proud high hills, and left their plun- 

 dered treasures in the bosom of the deep ocean buried, 

 while slowly that deep bottom grew shallow and shallower, 

 until the land and sea changed places. Gradually approach- 

 ed the more modern eras, successively of fishes, then of 

 reptiles, then of exogenous plants, then of birds, then of 

 mammals; while lastly the fervor of superficial heat receded 

 from the polar towards the equatorial regions, followed in 

 its retreat by immense glacier streams arising from the ex- 

 pansion of water into ice by crystallization. The glacial 

 period must necessarily succumb in its turn to Sol's perse- 

 vering beneficent reaction, the tropical regions emerged 



