DISCUSSION OF CORRELATION 729 



Cambrian formations in the Lake Superior country- discloses no 

 backwardness in re\asing correlations as fast as facts are found to 

 warrant revision. Seaman's discovery of a tripartite division in the 

 Marquette district was immediately recognized by the geologists of 

 the United States Geological Survey and was first pubKshed by 

 C. K. Leith in 1904/ with permission of Professor Seaman. Neither 

 may it be said that there is any delay in recognizing the significance 

 of the supposed new formation in the eastern Gogebic district. In 

 fact, the writer took some part in the field in the analysis of the 

 situation leading up to this discovery. It may be freely conceded 

 that in the past there was more emphasis on a given number of 

 series as a basis of correlation, but the basis of correlation has been 

 constantly widened by the addition of new criteria. It seems 

 pecuHarly inappropriate, therefore, to argue that what might have 

 been done in the past on the basis of a preconceived notion of a 

 nimiber of series should serve as a primary basis of classification 

 now when a much greater variety of facts is available. 



In short, the suggested changes in correlation seem to the writer 

 interesting possibiHties, for which e\'idence must be carefully looked 

 for in further geological work in this district, but that they are only 

 possibiHties and in the present state of knowledge cannot stand 

 against the general considerations above outhned. It should not 

 be overlooked that the new series suggesting these sweeping 

 changes is yet known in but a few outcrops in a limited area where 

 the folding and intrusion have been extensive, and that there is 

 distinct possibility that the formation may have been of only local 

 significance. 



In case the newly proposed classification can be estabhshed 

 it will be a welcome advance in our knowledge of Lake Superior 

 geology. The purpose of this argument is not to discourage an 

 attempt to make such an advance, but to indicate the difi&culties 

 inherent in the problem and the impossibihty in the present state 

 of knowledge of accepting an interesting hypothesis as a proved 

 fact. 



' C. K. Leith, Trans. Am. Inst. Min. Engrs., Lake Superior meeting, 1904. 



