554 



F. T. THWAITES 



PRE-CAMBRIAN SYSTEMS 



Base of the Paleozoic rocks. — The Paleozoic series rests upon a 

 rather irregular basement of pre-Cambrian igneous and meta- 

 morphic rocks. Older attempts'' to map this surface have not shown 

 nearly as many buried monadnocks as are now known. For the 

 most part these are composed of Huronian quartzite, not unlike 



TABLE VIII 



Partial Log of City Well No. it, Madison, Wisconsin 



Depth 

 (Feet) 



Sandstone, medium to fine, white 



Sandstone, medium to fine, white; some beds hard, calcareous, 



pink 



Sandstone, medium to fine, light gray 



Sandstone, coarse to medium, light gray 



Sandstone like above with layers of sandstone, fine, pink and 



green, hard, calcareous 



Sandstone, coarse to fine, light gray 



Sandstone, coarse to medium, light gray; layers of sandstone, 



fine, pink and green, hard, calcareous 



Sandstone, coarse to fine, gray 



Sandstone, coarse, gray; pyrite 



Sandstone, very fine to medium, gray, shaly, non-calcareous. . . . 



Sandstone, coarse to fine, gray, some layers pink 



Sandstone, very coarse to fine, gray 



Sandstone, medium to fine, gray 



Sandstone, medium to fine, pinkish gray 



Sandstone, fine, gray, shaly 



Sandstone, very coarse to fine, pink 



Sandstone, coarse to fine, gray 



Shale, dark pink 



Sandstone, very fine, pink 



Sandstone, coarse to fine, gray 



Shale, pink and red to pre-Cambrian 



Total thickness 



390 



450 

 475 

 520 



530 

 540 



560 



595 

 605 

 607 

 610 

 630 



645 

 650 

 680 

 685 

 690 

 695 

 715 

 720 



733 



that exposed at the surface near Baraboo and Waterloo, Wisconsin. 

 At a number of places in Wisconsin these buried mountains rise 

 high enough to cut off part or all of the water-bearing strata; such 

 is the case at Hartford, Kewaskum, Two Rivers, and in part of 

 Fond du Lac. 



Possible Keweenawan sandstone. — No igneous or metamorphic 

 rocks have ever been reached in northern Illinois, or on the Lake 



* I. A. Lapham, Geological map of Wisconsin, 1869. Samuel Weidman and 

 A. R. Schultz, op. cit., map. 



