THE BASEMENT COMPLEX 9 



Prior to the introduction of this term, in 1886, Lawson had proposed 

 the name "Keewatin" for a great series of roclcs, largely volcanic, which 

 occurs in the Lake of the Woods region. His reason for proposing the 

 name was that the series was different from any Huronian or Laurentian 

 series which had been described, and he was uncertain as to its strati- 

 graphical position. When the work of the United States Geological Sur- 

 vey was extended to the international boundary, the detailed work being 

 done by Leith, Clements, and Bayle}^, it was found that Lawson's Kee- 

 watin series is in the same position — indeed, is a continuation of the 

 Mareniscan of the United States. Since the term Keewatin was pro- 

 posed prior to that of Mareniscan, although the latter was first defined in 

 the broad sense, the International Committee, with my concurrence, ac- 

 cepted the former term to designate the ancient volcanic series of the 

 basement complex. 



Of tlie different geologists, Clements has made the most careful petro- 

 graphic study of the Keewatin, and his map of the Vermilion district 

 •shows the formation to consist of a great variety of basic and interme- 

 diate rocks, the major portion of which are volcanic rather than plutonic. 

 A peculiar ellipsoidal greenstone is especially characteristic and has a 

 widespread occurrence. My own general studies of the Keewatin, where 

 best exposed over broad areas in a number of districts, have led to the 

 conclusion that it is essentially a submarine volcanic group, although of 

 course including many intrusive rocks. 



AVhen the United States geologists (Clements, Leith, Bayley, and Mer- 

 riani) mapped the Vermilion district of northeastern Minnesota they 

 found that associated with the Keewatin is an iron-bearing formation 

 whicli is productive. The more closely the district was studied, the 

 plainer it appeared that the thick productive formation is in all probabil- 

 ity upon the top of the igneous rocks in some places between the two, 

 there being a slight erosion interval marking unconformity. Smaller 

 beds of iron formation material seem clearly to be within the Keewatin 

 greenstones. 



Later studies in Canada have shown that an iron-bearing formation 

 similar to that of tlie Vermilion district is widely associated with the 

 Keewatin, for example, in the Hiinters Island, Atikokan, Matawin, Mich- 

 ipicoten, and otlicr districts. 



THE HURONIAN SERIES 



Irving and Brooks found tlie series of the south shore above the base- 

 ment complex to consist dominantly of sedimentary formations such as 

 limestones, quartzites, slates, etcetera, which may be mapped stratigraph- 



