8 C. E. VAN HISE THE PROBLEM OF THE PRE-CAMBRIAN 



Azoic was applied. But Pumpelly, Marvine, Brooks, Irving, and Wright, 

 with unflagging energy and infinite patience, resumed on the south shore 

 of lake Superior the true stratigraphic methods of the great Canadian 

 geologists. The names of Pumpelly and Marvine must be connected 

 ever with the stratigraphy of the Keweenawan rocks. Their papers on 

 this series are classic today. Similarly the names of Brooks and Irving 

 must be associated always with the stratigraphy of the iron-bearing or 

 Huronian rocks. In this pioneer work Brooks wore himself out in ten 

 years, so that he never was able to resume active geological work. 



If one who was familiar with the Lake Superior region in these early 

 days, and therefore knows the conditions tinder which Brooks' and 

 Irving's work was done in an unbroken forest, will examine their geo- 

 logical maps of the Marquette, Menominee, and Penokee districts, he can 

 not but be filled with admiration at the amazing insight of these men, 

 who Avere able to put into a consistent story the scraps of geological his- 

 tory which they were able to gather from the occasional outcrops in the 

 wilderness. 



Brooks, Pumpelly, and Irving recognized the same major divisions on 

 the south shore of lake Superior which Logan and Murray had recognized 

 on the north shore of lake Huron. That is to say, there was a great com- 

 plex of basement rocks and above them essentially sedimentary series 

 which contain the iron and copper deposits. 



THE BASEMENT COMPLEX 



The lower or basement group was found to consist dominantly of gran- 

 ites and gneisses which were believed to be in the same stratigraphic posi- 

 tion as the similar rocks of the Laurentian of the north shore of lake 

 Huron. Irving also found on the south shore a series of dark gray and 

 green schistose rocks, proved by George IT. Williams to be largely of vol- 

 canic origin, which he recognized were structurally more closely asso- 

 ciated with the granite and gneiss called Laurentian than with the sedi- 

 mentary iron-bearing series. In this respect Irving made an advance 

 upon the work of Logan, who on the north shore of lake Huron placed 

 the equivalent rocks with the Huronian. 



Williams proved that the granites and gneisses of the basement series 

 intrude the schistose volcanic series, the relations being the same as those 

 which were later found to obtain on the north shore of lake Huron. Our 

 further studies show that this volcanic series is an extensive one. When 

 this fact was realized and it was appreciated that it was the oldest series 

 in the Lake Superior region, the term "Mareniscan" was proposed in 1892 

 to designate it.* 



•Bulletin no. 80, TJ. S. Geological Survey, p. 191. 



