EFFECTS OF THE POST-HURONIAN REVOLUTION 157 



the shallower water, we should expect the rate of chemical precipitation 

 of calcium carbonate at the bottom to be concentrated in the neritic 

 (epicontinental) and shallower bathyal regions, a total area of, say, 

 35,000,000 square miles. 



Let us assume that previous to the post-Huronian orogenic revolution 

 the whole area of the lands was 20,000,000 square miles, or about 20/55 

 of the present area. On the view that the ocean has had a nearly con- 

 stant volume from Huronian times to the present, it follows that the 

 Huronian sea was largely epicontinental for an area of more than 

 35,000,000 square miles ; so that the area of rapid chemical precipitation 

 of calcium carbonate was about twice as great as the possible present 

 area. Let us also assume that the post-Huronian revolution increased 

 the land area to 55,000,000 square miles, which is roughly the present 

 area of the lands. 6 



The annual rate of the supply of calcium to the ocean was, on these 

 assumptions, increased from (55/20 X 2=) 5.5 to (55/20 X 5 -(- =) 

 1-A+ times by the post-Huronian crustal movements. But the sea- 

 bottom area over which the chemical precipitation of calcium carbonate 

 was compelled was halved by those movements. Thus the post-Huronian 

 conditions favoring the possibility that a part of the river-borne calcium 

 could remain in solution in the ocean were from (5.5 X 2=) 11 to 

 (14X2=), 28 or more times more effective than the pre-Huronian 

 conditions. 



Although little stress can be laid on any particular figure embodied in 

 the foregoing conclusions, this rough analysis serves to illustrate the 

 strength of the probability that the prodigious crustal movements of the 

 post-Huronian and pre-Cambrian interval made a comparatively rapid 

 and quite drastic change in the chemical condition of the ocean. 



Analyses of the Ottawa Elver 



The view that the supply of calcium to the ocean reached a maximum 

 rate in post-Huronian and pre-Cambrian time is based on some specula- 

 tion. Apparently more certain are the grounds for believing that the 



6 Joly's well known estimate of the age of the ocean as about 90,000,000 years seems 

 much too low for the needs of the geologists. His view that the sodium borne into the 

 ocean by the rivers during past time is nearly all represented in the present sea-water 

 is apparently one of the soundest in dynamic geology. The chief source of doubt as to 

 the validity of his method of calculation consists in the obvious fact that it is not yet 

 possible to secure even an approximate idea as to the secular variation of the land 

 area in size. The age of the ocean would be greatly increased if account be taken of a 

 relatively small land area throughout much of pre-Cambrian time. To the present 

 writer Joly's estimate is of value in suggesting that the pre-Huronian land area was in 

 reality small. J. Joly, Scientific Transactions, Royal Dublin Society, vol. 7, 1899, p. 23. 



