R. A. Daly — Limeless Ocean of Pre-Cambr-ian Time. 115 



Time Place of the Great Unconformity.* 

 Cambrian Period. 



Diversified animal 

 types ; beginning 

 of lime secretion. 



Chief Fossils. — Cal- 

 eareo-chitinous 

 and calcareous. 



Lime salts suffi- 

 cient .for lime 

 secretion by ani- 

 mals. 



Land-areas proba- 

 bly diminished 

 but still large in 

 absolute meas- 



Botb chemical and 

 directly organic 

 calcium carbon- 

 ate ; chemical 

 magnesium car- 

 bonate in dimin- 

 ished proportion 



From Cambrian to Epoch of Colonization of General Sea-floor. 



Limey structures of 

 animals fully de- 

 veloped. 



Chief Fossils. - 

 careous. 



-Cal- 



Same as last 

 riod. 



pe- 



Land-areas, and 

 areas of weath- 

 ering limestone, 

 slowly though 

 not steadily in- 

 creasing. 



Same as 

 riod. 



last pe- 



Period Following Colonization of General Sea-floor. 



Same as last period. 



Gradual increase 

 of calcium sul- 

 phate in solu- 

 tion. 



Land-areas ap- 

 proaching max- 

 imum extent ; 

 Kivers drain 

 maximum area 

 of limestone. 



Directly organic 

 calcium carbon- 

 ate dominant ; 

 magnesium car- 

 bonate at its 

 minimum. 



*It may be noted that in British Columbia there is local conformity 

 between the Beltina beds and the beds corresponding to the Olenellus zone. 

 This is, of course, an exceptional relation between Cambrian and pre-Cam- 

 brian rocks as exposed on the continental plateaus. 



