J?. A. Daly — Limeless Ocean of Pre- Cambrian Time. Ill 



phate to the pre-Cambrian sea, we have conditions favorable 

 to the slow development of thick beds of iron carbonate or of 

 sideritic shales, etc. 



Origin of certain pre- Cambrian cherts and jaspers. — 

 Liebig states that the same alkaline carbonate lessens the solu- 

 bility of colloidal silica in water.* It is also a familiar fact 

 that this carbonate precipitates most of the silica from solutions 

 of water-glasses, silicate of sodium, silicate of potassium, etc., 

 substances which are present in river-waters. The suggestion 

 lies near that we may have here a partial explanation of the 

 puzzling cherts and jaspers so specially associated with the 

 Lake Superior ores. In this view they are due to the throw- 

 ing down of silica from river-waters relatively rich in dissolved 

 silica or silicates. As with the iron carbonate deposits these 

 precipitates would be but locally developed within the ancient 

 ocean-basin ; such, according to the accepted authorities, 

 seems to be the fact for both kinds of precipitate in the Lake 

 Superior district. 



The writer has but little first-hand knowledge of the district. 

 The discussion of the intricate facts of field observation as 

 detailed in the many able monographs on the iron-bearing 

 rocks is as difficult as the discussion of the obscure chemistry 

 of river-waters. The subject is here touched upon simply to 

 indicate a possible test of the main hypothesis of the present 

 paper ; all that appears clear from the foregoing brief consid- 

 erations is that, when we have final demonstration of the 

 origin of the " greenalite," siderite, and ferruginous chert of 

 the Lake Superior region, that demonstration may be found to 

 favor the thesis here suggested regarding the chemistry of the 

 pre-Cambrian sea. 



Origin of the petroleum and natural gas emanating from 

 pre-Cambrian sediments. — Finally, the hypothesis of an essen- 

 tially limeless sea during Eozoic times correlates well with the 

 undoubted fact that natural gas and petroleum are to-day 

 issuing from pre-Cambrian strata. An excellent example of 

 this is seen in the field now being prospected in the Flathead 

 Yalley of British Columbia, at points situated so far inside the 

 eastern limit of the Rocky Mountains as scarcely to allow one 

 to entertain the idea that these hydrocarbons really come from 

 Cretaceous or other fossiliferous formation which here underlie 

 the great Rocky Mountain overthrust. The entombment of 

 the carcasses of soft-bodied animals is, it is true, partly pre- 

 vented by their bacterial decomposition, but doubtless not 

 more so than by the steady removal of carcasses from the sea- 

 bottom by scavengers. Murray has shown that there" is, in the 



* Quoted from A. M. Comey's Dictionary of Chemical Solubilities, Inor- 

 ganic ; London, and New York, p. 360, 1896. 



