40-(10) MH5TEBAL PHYSIOLOGY. 



not intervene, or at best, plays but a secondary and in- 

 direct part through the products of its partial decay. 

 Besides what we have just called the organic circulation 

 of matter, there are three others which we may designate 

 as the terrestrial, the aerial and the oceanic circulations. 

 No one of these is independent of the others, and all of 

 them are, in fact, ultimately subordinated to the last 

 named ; yet each may be considered by itself, and will 

 be found to present a history of physiological processes 

 replete with interest and instruction. The terrestrial cir- 

 culation especially, as I shall endeavor to show, fre- 

 quently offers suggestive analogies to the circulatory 

 processes in plants and animals. It is, moreover, through 

 this circulation that some of the most important mineral 

 masses in nature have been generated, and deposits of 

 precious metals, ores and gems have been derived from 

 the great bulk of the earth's crust. The study of the 

 terrestrial circulation will thus introduce us to one of the 

 most important chapters in the chemical history of the 

 globe. 



Without attempting to trace the chemical elements of 

 our earth to the lire-mist or nebulous matter from which 

 a modern theory with great plausibility conjectures their 

 origin, and without inquiring into the chemistry of a cool- 

 ing globe, which however presents a legitimate held of 

 speculation, I invite you to follow me backwards in ima- 

 gination to a time which is sometimes called the Prima- 

 ry or Archaean period, or the Eozoic age, in geological his- 

 tory, when there were already a- solid and cooled earth, 

 land and an ocean, in the waters of which animal and 

 vegetable life may be supposed to have been not less abun- 

 dant than they are in our present seas. At this time the 

 oldest known series of rocks, that called the Laurentian, 

 to which belong the granite-like gneisses of the Highlands 

 of the Hudson, the Adirondack hills and the Laurentides 

 of Canada, from which this ancient series takes its name, 

 — was already in existence. While from the seas of that 

 time were being deposited the materials of a newer series 

 of rocks, we have evidence that already the beds of this 

 ancient gneisses were in their present contorted and folded 

 position and had the same mineral composition as to- 

 day. Interstratitied with them were already the crys- 

 talline limestone with graphite, and the great beds of 



