154 Climate^ Geography and Geology of Minnesota — Upham. 



Saint Lawrence limestone and Saint Croix sandstone, together 

 regarded as the equivalent of the Chazy ai;id Calciferous forma- 

 tions in the northeastern states and Canada, extending in south- 

 eastern Minnesota from the Kettle river and Taylor's Falls, south- 

 east to the lower portions of the Minnesota and Blue Earth 

 rivers, and occupying a considerable belt along the Saint Croix and 

 Mississippi rivers to the southeast corner of the state; the Potsdam 

 or Cupriferous formation, of lower Cambrian age, consisting of 

 red sandstone, conglomerate and trappean rocks, on the shore of 

 lake Superior, and in Pine, Chisago and Kanabec counties, but in 

 southwestern Minnesota being mainly red quartzite, exposed near 

 New Ulm, and thence westward to Pipestone and Rock counties, 

 in the southwest corner of the state; and the Archaean system, 

 divided into three parts, namely. Upper Gneisses, Taconic and 

 Laurentian, together covering more than half of the state, reach- 

 ing on the international boundary from the Lake of the Woods 

 east to lake Superior, and extending thence southwest to the Min- 

 nesota river between Big Stone lake and New Ulm, but terminat- 

 ing twenty or thirty miles southwest of this river. 



19. The glacial geology: showing post-glacial alluvium, to 

 which is referred the stratified clay bordering the Red River of the 

 North, apparently deposited after lake Agassiz was drained to 

 Hudson bay; modified drift or stratified gravel, sand and clay, 

 washed from the ice-sheet and assorted and deposited by the 

 streams produced in its melting; loess, belonging to the modified 

 drift, extending from the Missouri river over western Iowa and 

 into Rock county in the southwest corner of Minnesota; till, or 

 bowlder clay, covering the greater part of the state, mostly having 

 a moderately undulating surface; terminal moraines, belts of hilly 

 and knolly till, with associated deposits of modified drift, accumu- 

 lated along the margin of the ice-sheet of the last glacial epoch, 

 including, besides the moraine found at the extreme limit reached 

 by that ice-sheet ten others indicating successive stages in its 

 recession; glacial striae, having a southwest course from lake 

 Superior to the Mississippi river, over which region is spread a red 

 till with no limestone, but in the west part oi the state running 

 to the south and southeast, the till there being gray or blue with 

 much limestone; changes in the currents of the ice-sheet during 

 its recession, shown by the course of the successive morainic belts, 

 he most notable change being the extension of the western ice- 



