JR. A. Daly — Limeless Ocean of Pre- Cambrian Time. 99 



have been initiated the epoch in which an indefinitely continu- 

 ous 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 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 radi- 

 cals 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.* 



Toward the close of Eozoic time there occurred one of the 

 world's greatest mountain-building revolutions. Very exten- 

 sive mountain-ranges were then erected and the continents 

 grew to large size. In a monograph summarizing some of 

 Walcott's researches on the Cambrian formations of North 

 America, the author writes : 



"The continent was well outlined at the beginning of Cam- 

 brian time ; and I strongly suspect, from the distribution of the 

 Cambrian faunas upon the Atlantic coast, that ridges and bar- 

 riers of the Algonkian continent rose above the sea, within the 

 boundary of the continental plateau, that are now buried beneath 

 the waters of the Atlantic. On the east and west of the conti- 

 nental area the pre-Cambrian land formed the mountain region; 

 and over the interior a plateau existed that at the beginning of, 

 or a little before, Upper Cambrian time was much as it is to-day. 

 Subsequent mountain building has added to the bordering moun- 

 tain ranges, but I doubt if the present ranges are as great as 

 those of pre-Cambrian time that are now known only by more or 

 less of their truncated bases. The Interior Continental area was 

 outlined then and it has not changed materially since. Its 

 foundations were built in Algonkian time on the Archean base- 

 ment, and an immense period of continent growth and erosion 

 elapsed before the first sand of Cambrian time was settled in its 

 bed above them."f 



Following the last world-wide, orogenic paroxysm of pre- 

 Paleozoic time, there was a long interval of more or less per- 

 fect baseleveling. In the process thousands of cubic miles of 

 rock were weathered and a large proportion of their mass went, 



*Cf. Murray and Irvine, Proc. Royal Society of Edinburgh, vol. xvii, p. 90, 

 1889. 

 fl2th Annual Report, United States Geological Survey, p. 562, 1891. 



