100 THE GEOLOGY OF MINNESOTA. 



[Warren, 186*. 



The lake Superior trap rocks, carrying native copper, he assigned to 

 the age of the Potsdam.* Those carrying the sulphurets of copper, he 

 placed in a different, and older system, the Huronian, after the generaliza- 

 tion of Bigsby and Logan. The quartzyte at Pokegama falls, he styled 

 Potsdam. 



With the exception of occasional misapprehensions of minerals, Mr. 

 Whittlesey's brief notes, with the accompanying rough illustrations, consti- 

 tute a valuable and correct geological epitome of the northern part of Min- 

 nesota, from Encampment river on the east to the Grande Fourche, or Big 

 Fork river, on the west. It embraces also short chapters on the general 

 geology, the phenomena of the drift period, general elevations in Minne- 

 sota, fluctuations in the level of the lakes, the climate, and the cost of 

 mining copper. 



GENERAL G. K. WABREN ON THE MINNESOTA VALLEY. 



The United States government detailed General Warren in 1866, for 

 the survey of the upper Mississippi, Minnesota and Wisconsin rivers with a 

 view to the improvement of navigation and the construction of bridges 

 which should afford the least possible obstruction to navigation. The work 

 on the Minnesota was continued in 1867 and 1868. In the annual report 

 of the Chief of Engineers for 1868, is found General Warren's first 

 published general expression of his views concerning the physical features 

 of the Minnesota valley, although they were in part presented in Sen. 

 Ex. Doc. No. 58, 39th Congress, 2nd Session, dated January 21, 1867. 

 His final report, in extenso, was not rendered till 1874, owing to the inter- 

 vention of other duties, and is to be found in the appendix to the report of 

 the Chief of Engineers for that year.f Part II of this report is an essay 

 concerning important physical features exhibited in the valley of the Minnesota 

 river, and upon their signification. This is illustrated by several maps, plates 

 and diagrams, and accompanied by a detailed description of the valley by 

 his assistant, Mr. C. E. Davis. 



The main points brought out in this essay, are ; 1st, that the Minnesota 

 valley was formerly the course of a great river; 2nd, that this river 



*On page 7 Mr. Whittlesey makes the following remark concerning the rocks of the Mesabi : " In many cases the 

 yenite and granite appear to be more recent than the metamorphic slates, having all the appearance c,f intrusive rocks." 



t^ee also the American Aatmalist, November 1868, for a summary of a paper read by Gin. Warren before the 

 American Association for the Advancement of Science. 



