I'LATK I, XVI. 



SOUTH PART OF ST. Louis COUNTY, 1899. N". H. WINCHELL. 



The oldest rocks in the area of this plate, geographically known as the Thomson 

 slates, are those seen in small scattered outcrops in the valley of the St. Louis river, 

 in towns 50-17, 51-18 and 51-19. These probably belong to the Keevvatin, while 

 those seen in town 49-15 are supposed to be of the Animikie. Overlying these rocks 

 is a nonconformable, coarse conglomerate (Puckwunge) seen in the valley of the St. 

 Louis river at the water's edge in sec. 1, T. 48-16, just outside of the area of this plate. 

 This is the bottom of the Potsdam and was followed by Manitou eruptive action in 

 the near vicinity, as evinced by the nature of the fine conglomerates and sandstones 

 that overlie it, although none of those traps are seen here interbedded with those 

 sandstones. They are supposed to lie further south and east, covered by the allu- 

 vium of the St. Louis river and by lake Superior. In the area of this plate these 

 Manitou eruptives are represented by the diabase dikes that cut the older (Cabotian) 

 traps seen at Duluth and along the shore further east, as far as to Splitrock river. 



Between Short Line park and Duluth the gabbro shows diabasic characters, and 

 is believed to contain both the Beaver Bay diabase and the gabbro proper, the former 

 being a great surface flow derived from the latter; the surface lavas at Duluth being 

 still more remote eft'usives and perhaps considerably later than the gabbro, but all 

 antedating the Puckwunge conglomerate. 



One of the moraines of the Lake Superior ice-lobe, named Highland moraine 

 by Mr. Elftman, passes through this area. It lies south of the Cloquet river and is 

 crossed by the St. Louis river between Gowan and the Carlton county line, but 

 extends into Carlton county, and Aitkin county south of Sandy lake. At the time 

 of the formation of this moraine the ice dammed back the waters of the upper St. 

 Louis river, forming a glacial lake which covered the great swamp that occupies the 

 northwestern half of this area,, extending also much further north and east. This 

 was the infant progenitor of lake Superior. It had its outlet westward into the 

 Mississippi, probably by way of the valleys of the East and West Savanne rivers, 

 across a low divide, which later was the route of the Hudson Bay company's fur 

 traffic for many years. Throughout the area of this old lake the till is covered either 

 with laminated clays or with washed sands. This glacial lake has likewise never 

 been named. In recognition of the faithful and indefatigable service of one of the 

 assistants on the Minnesota survey in the glacial geology of the state, it is proposed 

 to call this lake Upham. That the waters that laid the stratified clays of this district 

 derived their sediments from the red shales and sands of the Lake Superior basin, 



