242 F. W. SARDESON THE BEDSTONE QUARTZITE 



rapid weathering away of these it came to again stand as a prominence 

 above them. In Cambrian time it was met by the advancing ocean, which, 

 instead of demolishing it, flowed around it, leaving a shore deposit of 

 gravel even on its landward side. For several geologic ages the Redstone 

 quartzite then stood as a great rock above a neighboring valley, much the 

 same as the Baraboo quartzite of Wisconsin now stands. During Cre- 

 taceous time the river valley passing its south side filled with delta de- 

 posits, but probably leaving the top of the Eedstone quartzite exposed well 

 above the sedimentation plain. During the Tertiary, land erosion again 

 made a valley, which was some 200 feet deep, crossing the granitic area 

 to the north of the Eedstone hill. During Pleistocene or Quaternary 

 time the top of the quartzite was twice crossed by great glaciers. From 

 the glaciers the rock received slight grooves and striations which are still 

 clearly seen. They bear south 33 degrees east. The glaciers also spread 

 sheets of till over it, although in inter-Glacial and in post-Glacial time 

 erosion in part at least bared it again. 



Although the geologic formations are all of scientific interest and have 

 been described in detail in the preceding pages, the Redstone quartzite 

 stands out as the most prominent feature in the geology of the area here 

 described. 



References 



1. Shumard, in Owen's Report of a geological survey of Wisconsin, Iowa, and 



Minnesota, 1852. 



2. James Hall: Notes upon the geology of some parts of Minnesota, etc. 



Transactions of the Philosophical Society, volume 1.3, new series, 1869. 



3. N. H. Winchell: Geological and Natural History Survey of Minnesota. 



Annual report for 1873. 

 Jf. Leo Lesquereux: Cretaceous flora. U. S. Geological Survey of the Terri- 

 tories, volume vi, 1874. 



5. N. H. Winchell: Geological and Natural History Survey of Minnesota, 



volume i, 1884 ; volume ii, 1888. 



6. Warren Upham : Loc. cit., volume i, chapter xx ; volume ii, chapter v. 



7. R. D. Irving and 0. R. Van Hise: Secondary enlargements of mineral 



fragments in certain rocks. U. S. Geological Survey, Bulletin 8, 1884. 



8. Leo Lesquereux: Geological and Natural History Survey of Minnesota, 



volume iii, 1895, chapter i. Cretaceous fossil plants from Minnesota. 



9. N. H. Winchell: A rational view of the Keweenawan. American Geolo- 



gist, volume xvi, 1895, pages 150 to 162. 



10. C. W. Hall: The gneisses, gabbro-schists, and associated rocks of south- 



western Minnesota. U. S. Geological Survey, Bulletin 157, 1899. 



11. N. H. Winchell: Geological and Natural History Survey of Minnesota, 



volume vi, 1901. 



