REPORT OF THE CHIEF ASTRONOMER 649 



SESSIONAL PAPER No. 25a 



be slowly destroyed. How extensively the radical was replaced by tbe volcanic 

 emanation of sulphurous gases from the earth's interior cannot be demonstrated. 



Yet more obscure are the reactions which might have led to the more 

 permanent binding of the sulphuric acid and chlorine radicals to magnesium 

 introduced to the sea in the form of the carbonate by the rivers. The chlorine 

 radical freed from calcium chloride might have become in part gradually bound 

 to sodium. 



The utmost efforts of chemists may 'be unable to determine fully the exact 

 reactions that take place in so complex a solution as sea water, but it seems fair 

 to grant the possibility of some such rearrangements among the ions of the Eozoic 

 sea water. Sodium and magnesium salts are the dominant salts in the sea to-day 

 and it is simplest to suppose that they have become so because of a slow evolution 

 of an ocean tending towards a maximum ionic stability. The sulphates are 

 to-day relatively subordinate because of the very extensive precipitation of 

 insoluble sulphides and carbonates, directly or indirectly through the chemical 

 influences of living or putrefying animals. 



If, finally, the acid radicals became either destroyed as such or permanently 

 bound to bases more powerful than lime, the concentration in the sea water of 

 calcium carbonate introduced by rivers first became possible. Then and then 

 only might have been initiated the epoch in which an indefinitely continuous 

 series of lime-secreting animals could be evolved. The beginning of this epoch 

 might have been near the opening of the Cambrian period. 



Or, thirdly, we may suppose — and this seems to be the more probable 

 alternative — that a relatively sudden influx of river-borne calcium salts might 

 produce an excess of them in the sea-water solution over that amount which 

 hitherto was kept continuously precipitated by organic decay on the sea bottom. 

 In this case it is simplest to postulate that acid radicals were still free in some 

 measure to convert the river-borne carbonates into sulphates or chlorides. By 

 such reactions the calcium would appear in those salts which are now normally 

 used by lime-secreting animals; the animals would then have a much more 

 abundant source of calcium for the elaboration of hard parts than if the much 

 less soluble carbonate only were present.* 



Effects of the Huronian Orogenic Revolution. 



Toward the close of Eozoic time there occurred one of the world's greatest 

 mountain-building revolutions. Very extensive mountain-ranges were then 

 (at the beginning of the ' Eparchean Interval ') erected, and the continents 

 grew to large size. In a monograph summarizing some of Walcott's researches 

 on the Cambrian formations of North America, that author writes : 



1 The continent was well outlined at the beginning of Cambrian time; 

 and I strongly suspect, from the distribution of the Cambrian faunas upon 

 the Atlantic coast, that ridges and barriers of the Algonkian continent rose 

 above the sea, within the boundary of the continental plateau, that are now 



* Cf . J. Murray and R. Irvine. Proc. Roy. Soc, Edinburgh, Vol. 17, 1889, p. 90. 



