DISCUSSION. 



Professor C. R. Van Hise : If I were personally concerned only, I should 

 not occupy time by going into this question at all. I do not feel that my 

 familiarity with northeastern Minnesota would warrant it. Many geologists 

 know that Professor Irving gave a great deal of his time for several years 

 to an investigation of the formations of northeastern Minnesota. During 

 this time he was assisted by Mr. W. N. Merriam and Mr. W. M. Chauvenet, 

 so that the amount of time he has put upon this area, through his representa- 

 tives and in person, I can safely say far exceeds that of any other single individ- 

 ual; and I may say I think, although I am not so positive as to this, that no 

 other survey has given the region as much time as Professor Irving's. 



Now, many of Professor Irving's conclusions are altogether different from 

 Dr. AVinchell's. Dr. Wiuchell began by stating that he intended to give 

 observations only. It seems to me before he had finished he put in many 

 theoretical conclusions. If the diagram drawn on the board (fig. 7) is not 

 a theoretical conclusion, involving as it does a thickness of sediments of over 

 100,000 feet,* I do not understand in what theory differs from fact. As to 

 the distribution of the rocks outlined by Dr. Winchell, I can bear testimony 

 to its general correctness, with the exceptions that I would not designate 

 certain of the rocks by the names which he gives them and would differ 

 from him as to the character of some of them, whether they are crystalline 

 schists or semi-crystalline elastics. 



As to the correlation of these series, Professor Irving held tentatively, not 

 dogmatically, that the Animike series is the equivalent of certain sediment- 

 ary rocks in the Vermilion lake section as drawn by Dr. Winchell. As to 

 who first discovered the unconformity below the Animike I will not farther 

 discuss, but will only say that I know positively that Professor Irving recog- 

 nized it at the time he read his paper before the National Academy, in the 

 spring of 1887.f He recognized it to its fullest extent, and in this matter 

 agreed fully with Dr. Winchell. The chief point of difference is the relation 

 of the Animike rocks and the rocks which bear the iron ores at Vermilion lake. 

 These latter beds are in good part jaspery, and they are associated with rocks 

 which are distinctly semi-crystalline, yet are in places actually conglomer- 

 ates. The whole area west of the Animike series has been carefully gone 



* Report upon a Geological Survey in Minnesota during the season of 1886 : Alexander Winchell : 



is similar to 

 i aggregate of 



scnlVts may be added the observed breadth of the gneiss on the north side, making a total thick- 

 ness of 106,204 feet," , ..„...,.,, 



f Professor Irving and Mr. W. M. Chauvenet examined together the exposures at Ounriint lake 

 and saw evidence of the unconformity referred to in September, 1883. Professor Irving in his field- 

 note book (Sept. 6, 1883) sums upas follows: "The whole appearance [of the] topography, lithology, 

 persistence of rock beds is certainly suggestive of an unconformity here." Says Mr. Chauvenet in 

 his field notes : " There is here evidence of total unconformity." 



(391) 



