OF IOWA, WISCONSIN, AND MINNESOTA. 



145 



power which has brought these detached masses of granite rocks into their present 

 position, is floating ice — ice drifted by currents setting in from the north, before the 

 land emerged from the ocean, in the same manner as, at the present time, thousands 

 of tons of rock are precipitated on the bed of the Atlantic Ocean from icebergs, 

 which annually work their way from the north, and melt in southern latitudes. 

 No mere currents appear at all adequate to convey such heavy blocks across valleys, 

 and over hills, to a distance of hundreds of miles from the parent rock. Their 

 isolated position in the prairie also indicates that they were dropped into their pre- 

 sent situation, rather than rolled into it. Under the latter supposition, even if it 

 were possible, they would probably be closer together, and more regularly assorted 

 as to size. 



SECTION II. 



THEIR PALAEONTOLOGY. 



No fossil remains of any kind have been observed either in the drift deposits or 

 in the stratified rocks intervening between the Protozoic Sandstones of Wisconsin, 

 and the Crystalline Rocks. 



Hereafter, especially in making deep cuts for railroads or similar improvements, 

 such may come to light, in some of the superficial drift formations, since these have 

 furnished, in Canada, and, in some rare instances in Europe, a few organic exuviee. 



SECTION III. 



TtlEIR MINERAL CONTENTS. 



Isolated masses of native copper, and small portions of other ores, are not of 

 unfrequent occurrence in and amongst the numerous boulders accumulated in the 

 river beds. 



All appearances go to prove, that these ores have a common origin with the 

 accompanying erratics ; or, in other words, that they are no longer in place, but 

 have been transported to greater or less distance, from the trap ranges, where they 

 originated, to their p resent location. 



The drift deposits are, therefore, but the secondary repositories of these ores, 

 which occur over their surface, at wide intervals. It is not within reasonable 

 expectation that they should be found in quantities sufficient to justify the expense 

 of searching them out, and collecting them together, from their distant and scattered 

 localities. 



Indications of ore in place were occasionally observed embedded in the substance 

 of granite, syenite, and greenstone, on several branches of the Chippewa. But these 

 have almost uniformly proved to be mere varieties of iron pyrites, in which analysis 



has failed to detect any admixture of metals more valuable than iron. 



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