KANSAS GLACIATION 501 



Illinoian, and later icefields, to be carried forward until deposited by the 

 final melting and retreat of the ice-border. Only where rock formations 

 of restricted area have peculiar characters by which their boulders can be 

 identified with certainty as distinct from all similar boulders supplied by 

 other formations and districts is it possible to affirm positively the dis- 

 tance of their transportation. 



Big Stone and Otter Tail counties, of western Minnesota, have rare 

 granite boulders with included fragments of hornblende schist, 6 like much 

 of the granite forming the Giants' or Mesabi range, which was probably 

 their source. These boulders appear to have been carried about 200 miles 

 southwest and west-southwest. Their glacial journey ran athwart the 

 southeastward courses of the predominant Keewatin ice currents and out- 

 flow during the Kansan and later glaciation in that district, so that we 

 must ascribe their transportation to the earlier Nebraskan stage. It was 

 probably contemporaneous with the Patrician ice currents which spread 

 from north of Lake Superior and carried their drift nearly or quite to the 

 Ohio River, as before noted. 



In Lucas County, of southern Iowa, a mass of drift copper weighing 

 more than 30 pounds 7 undoubtedly was borne by the currents of the ice- 

 sheet about 600 miles, from the present copper mining region south of 

 Lake Superior or from Isle Boy ale, first southwestward and later south- 

 ward through eastern and southern Minnesota, passing west of the Wis- 

 consin driftless area. Its journey probably was accomplished mostly dur- 

 ing Nebraskan time. 



The farthest recognized origin of rock fragments in the drift of our 

 continental ice-sheet, recorded in part by Dr. Robert Bell, of the Cana- 

 dian Geological Survey, whose observations are supplemented by the 

 present writer, is from James Bay southwest to North Dakota and Minne- 

 sota. The rock is "dark grey, granular, siliceous felsite or greywacke, 

 . . . characterized by round spots, from the size of a pea to that of a 

 cricket ball or larger, of a lighter color than the rest of the rock, which 

 weather out into pits of the same form/' It occurs as the bedrock, ac- 

 cording to Dr. Bell, on Long Island, off Cape Jones, on the east coast of 

 Hudson Ba}f, where it is narrowed to form James Bay, having there a 

 southwestward strike and probably continuing under the sea for some 

 distance in that direction. He noted that the abundance of pebbles and 

 boulders of this rock is the most remarkable feature of the drift on the 



a Geological Survey of Minnesota. Final Report, vol. i. 1884, p. 626 ; vol. ii. 1888, 

 p. 551. 



7 C. A. White : Geology of Iowa, 1870, vol. i, p. 96. 



