THE PROTEROZOIC ERA 55 



the Algonkian) and iron ore are rarely ever known to have been 

 formed except through the agency of organisms. 



Since the great masses of Proterozoic sediments are of quite 

 the usual sort like those formed in later eras, and since life surely 

 existed, we can be certain that the climate of the time was favor- 

 able for the operations of ordinary geologic processes and hence 

 not fundamentally different from that of comparatively recent 

 geologic time. 



According to a discovery made a few years ago, there is posi- 

 tive evidence for considerable glaciation in Canada during early 

 Algonkian time. Conglomerate beds at the base of the Huronian 

 are regarded as of glacial origin since there are " angular and sub- 

 angular boulders of all sizes up to cubic yards, enclosed in an 

 unstratified matrix. These boulders are often miles from any 

 possible source. Recently, striated stones have been broken out 

 of their matrix in the Lower Huronian of the Cobalt-Silver region, 

 giving still stronger proofs that the formation is ancient boulder 

 clay." l A climatic condition favorable for glaciation so early in 

 the earth's history is, to say the least, distinctly opposed to ideas 

 of climate of such early geologic time based upon the Laplacian 

 hypothesis of earth origin. 



Economic Products. — The greatest iron mining region in the 

 world is the Lake Superior district in Minnesota, Michigan, and 

 Wisconsin. Some of these iron ores are in the Archean, and some 

 in the older Huronian rocks, but the principal deposits are in the 

 Upper Huronian. These iron ores occur as thick beds in the sedi- 

 mentary series. Often the iron ore deposits have been enriched 

 by the work of underground waters. The Lake Superior district 

 produces many millions of tons of iron ore, or far more than the 

 production of any foreign country. 



The greatest deposits of native copper in the world are in the 

 Keweenawan series on Keweenaw Point, Michigan. Copper has 

 been found in small quantities in the lava beds, and underground 

 waters have dissolved out this copper and deposited it in more 

 concentrated form in fissures and openings of the rock, and also in 

 porous conglomerates. Immense quantities of native copper have 

 been mined here during the past forty years. 



» A. P. Coleman: Jour. Geol, Vol. 16, p. 149. 



