130 Wisconsin Academy of Sciences, Arts, and Letters. 



years, brief notices have appeared in various journals and re- 

 ports, but no careful investigation of the localities in question 

 seems ever to have been attempted. In most of these notices, 

 or rather in most of those that are not absurdly inaccurate in 

 their statements and wild in their ideas, the main point under 

 discussion has been the relative age of the metamorphic strata. 

 Do they, or do they not, antedate the Potsdam period ? Are 

 they the results of local metamorphism on the Potsdam sand- 

 stones, or are they the remnants of pre-existing rocks ? The 

 advocates of the former theory have had the last word in the 

 discussion. 



The facts recorded in the present article are the results of a 

 series of visits made to the localities by the writer, during the 

 months of September, October and November of this year 

 (1871,) and they will, I think, be seen to prove beyond all 

 doubt or cavil, that the quartzites and schists antedate entirely 

 the Potsdam epoch, i. e., are either Huronian or Lauren tian in 

 age. 



Of all of the notices mentioned, none are more than brief 

 mentions and only a few seem to have any value at all. Dr. 

 Shummard, in Owen's report on Wisconsin, Iowa and Minne- 

 sota, makes the first mention of the quartzite. He gives no 

 opinion. Dr. James G. Perceval, in the report of progress of 

 the Wisconsin survey for 1856, refers again to the quartzites, 

 calling them merely " metamorphic sandstones," but intimating 

 that they result from a change on the Potsdam sandstones. Mr. 

 James Hall, in his report of progress to the Grovernor of Wis- 

 consin for 1860, gives by far the most accurate description I 

 have been able to find. He refers the quartzites unhesitatingly 

 to the Huronian — but gives no proofs whatever. His pam- 

 phlet did not fall into my hands until after my own investiga- 

 tions were entirely completed. In the first volume of his final 

 report, Mr. Hall again mentions the quartzites, but still more 

 briefly, expressing the same opinion as before, and still giving 

 no proofs. In 1864 there appeared in the American Journal of 



