OF WISCONSIN AND MINNESOTA. 



105 



dykes, are in a perfect state of preservation,* and the strata themselves have no dip 

 perceptible to the unassisted eye in the hillside where they are exposed. 



Section No. 3, showing the succession of the rocks as they occur from the mouth of 

 the St. Croix, terminates with the above trap ranges on the north, and exhibits 

 their position in connexion with the adjacent fossiliferous strata above described. 



Drift and Crystalline Rocks between the Falls of St. Anthony and Grow Wing. — On 

 the 28th of May, 1848, I reached the northern limit of the survey of 1847. Here 

 I left the corps destined for the St. Peter's, to prepare for the ascent of that river, 

 while I proceeded, accompanied by Dr. Norwood, up the Mississippi to the mouth 

 of the Crow Wing, there to engage the necessary voyageurs, purchase canoes, and 

 fit out generally for our separate routes to the north. 



On my way to Crow Wing, but still better, on my return route down the channel 

 of the Mississippi, I had an opportunity to observe what I had never been able 

 satisfactorily to gather from the reports of other explorers ; that is, the exact locality 

 where the crystalline rocks are first seen unequivocally in place, after leaving the 

 fossiliferous limestones of the Falls of St. Anthony ; as well as the place where the 

 last of the sedimentary strata are visible, before being entirely hidden from view 

 under the superincumbent drift. 



In the cut of a rivulet which enters the Mississippi, three miles above the Falls, 

 a white loose sandstone is exposed, the same formation (St. Peter's Sandstone, F. 

 2, c) which forms the lower eighteen feet of the sections at the Falls of St. 

 Anthony. Scattered along the declivities of the bank, are also fragments of the 

 overlying fossiliferous limestone. This is the last exposure of these rocks I was 

 able to discover in ascending the Mississippi. Beyond this, they are lost to view 

 under the drift. For a distance of over sixty miles, by the land route, or nearly 

 eighty by the course of the stream, no rocks were seen unequivocally in place ; but 

 in many of the intervening rapids, as, for instance, those above the mouth of Elk 

 River,"j" there are protruding masses of granitic rocks, which, though they appear 

 like large erratics, resting in the river bed, are probably either in place or not far 

 removed from the parent mass. 



At the Osakis Rapids, however, is a beautiful variety of pink granite, and gray, 

 syenitic granite, with veins of a closer grained quartzose granite, well exposed in 

 place, on the east bank of the river, with a bearing of 70° to 80° east of north. 

 Associated with these are subordinate beds of hornblende and greenstone. 



Through the kindness of Colonel Fletcher, I obtained a portion of a specimen of 

 native copper, said to have been picked up on the Osakis Rapids. I regret not 

 having been able to see the whole of the original specimen, which was said to weigh 

 ten pounds, as I could then have formed a more correct opinion as to its being a 

 drifted mass, or having originated in veins in the rocks of these rapids. From all 



* In some the nacre is entire. Remains of the same kind of shells can also be detected in fragments 

 enclosed in the trap, and so much altered as to be distinguished with difficulty from the surrounding 

 greenstone. 



f The Elk lliver referred to comes in on the east side, beyond Rum River. Another of the same name 

 is laid down on Nicollet's map, higher up, and coming in from the west. 



