536 Transactions of the Canadian Institute. [Vol. VII. 



To the biologist the value of the question obtains from a dififerent 

 point of view. The sea is the original home of all life on the globe, 

 and it was in the sea that the differentiation between animal and 

 vegetable life, as well as the evolution of the great divisions of the 

 animal kingdom were effected. Indeed the great events in the evolu- 

 tion of animal forms have been rendered possible by changes which 

 have taken place in the composition of ocean water. These changes 

 have modified organisms, and have created conditions which have 

 served as factors in directing the course of development. This may be 

 specially illustrated by reference to the case of the calcium salts in sea 

 water. That the earlier Archaean seas contained comparatively small 

 quantities of calcium compounds seems to be clearly indicated by the 

 fact that in pre-Cambrian strata the limestone deposits are very limited, 

 not more than two per cent, of the thickness of the beds, the Huronian 

 portions of which, now generally recognized as of sedimentary origin, 

 are, according to Lawson,* over 50,000 feet in thickness. The small 

 amount of limestone deposits could not have been due to the absence 

 of living organisms, for the oldest Cambrian beds contain Trilobites and 

 Brachiopods, and such highly specialized forms postulate a long course 

 of pre-Cambrian life. The very fact that the Brachiopods of the early 

 Cambrian were largely those provided with a horny or chitinous shell, 

 indicates that all the animal forms of the preceding period had imper- 

 fectly acquired the lime " habit," which, one may reasonably believe, 

 would have earlier made its appearance had calcium salts been present 

 in considerable quantities in ocean water from the first. It is perhaps 

 due to the absence of this lime " habit " that fossils do not obtain in 

 pre-Cambrian strata. 



Once, however, the lime " habit " was acquired, through adaptation 

 of the animal cell to its environment, the course of development became 

 accelerated, and the evolution of the higher types of Invertebrate life, 

 as well as all the forms of Vertebrata, became possible. The Vertebrate 

 skeleton, and all that it implies in evolution, is, therefore, a result of the 

 gradual increase in the quantity of calcium in the oceans of the pre- 

 Cambrian period. 



To both the geologist and the biologist the history of the chemistry 

 of the ocean has recently acquired an additional interest from the 

 attempt made by Jolyf to determine the age of the earth, who uses for 

 that purpose as factors the amount of sodium now in the ocean, and that 



* Geol. Survey of Canada, 1887, pp. loi and 102, F. 



+ All Estimate of the Geological Age of the Earth. Trans. Roy. Dublin Soc, Vol. 7, (Ser. 2), 

 1899, p. 23. 



