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 PALAONTOLOGY. 
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 exuvie. 
SECTION IIL 
THEIR 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. 7 
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 present 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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