84 EDWARD ST EI DT MANN 



R. A. Daly' believes that the pre-Cambrian ocean probably con- 

 tained less lime than the present ocean, for the following reasons: 

 the sea must have been fresh or nearly fresh initially; the pre- 

 Cambrian rivers probably carried less Hme because the lands of that 

 time did not possess the great development of Hmestone of the 

 present; the lime contributed to the sea was probably precipitated 

 by ammonium carbonate generated through the decay of organisms 

 which accumulated on the sea bottom because of the lack of scaven- 

 gers. The field evidence which he cites in favor of this hypothesis 

 is the fineness of grain of many undisturbed pre-Cambrian dolomites 

 which he believes is indicative of chemical precipitation, and the 

 general scarcity of fossils in pre-Cambrian rocks, which he ascribes 

 to the lack of Hme in the sea from which organisms could obtain the 

 materials for shells and hard parts. 



Evans^ believes that the sudden appearance of the Cambrian 

 fauna may have been due to causes very similar to those which gave 

 rise to the sudden appearance of the Tertiary fauna. These periods 

 were preceded by great uplift of the lands, vulcanism, and wide- 

 spread aridity. The record of the evolution of life immediately 

 preceding them is therefore largely lost or inaccessible. 



Harder^ states that the pre-Cambrian manganese ores of the 

 United States are found in association with the, hematite deposits of 

 the Lake Superior region; as manganiferous zinc ores at Franklin 

 Furnace, N.J.; and in the metamorphic rocks of the Piedmont 

 region of Virginia, North Carolina, South CaroHna, and Georgia. 



Hayes" states that the pre-Cambrian iron ores of the Lake 

 Superior region furnish about 80 per cent of the annual ore produc- 

 tion of the United States. 



The iron formations from which the ores were derived are 

 sedimentary deposits, consisting mainly of cherty iron carbonates, 



' R. A. Daly, "Some Chemical Conditions in the pre-Cambrian Ocean," Conipte 

 Rendu, XI. Congres Geologique International, 1910, pp. 503-9. 



== John W. Evans, "The Sudden Appearance of the Cambrian Fauna," Compie 

 Rendu, XI. Congres Geologique International, pp. 543-46. 



3 Edmund Cecil Harder, "Manganese Deposits of the United States with Sections 

 on Foreign Deposits, Chemistry, and Uses," Bull. 427, U.S. Geological Survey, 1910, 

 pp. 298. 



4 C. W. Hayes, "Iron Ores of the United States," Bull. 394, U.S. Geological 

 Survey, 1910, pp. 76-84. 



