166 GEOLOGY OF EASTERN WISCONSIN. 



composed almost exclusively of quartzose saud, and one whose waters 

 elsewhere contain rather less than the usual quantity and variety of 

 salts found in our native waters. But we must consider that there is 

 here a depression of the strata, the sandstone being here lower by sev- 

 eral hundred feet than it is either north, south or west, and it is not 

 known to outcrop anywhere to the eastward, though the strata above 

 and below again come to the surface in Canada. 



The facts of the case warrant us in believing that there is no escape 

 for the waters in that direction. We have then here a basin reaching 

 himdreds of feet below the ocean level. Its waters have no outlet 

 and no escape except by the slow process of diffusion and percolation 

 through almost impervious strata. 



That the water should, under these circumstances, become highly 

 charged with saline ingredients is not at all remarkable, though the 

 facts are of an exceedingly interesting nature. 



The well at Janesville is located upon the Fair Grounds, at an ele- 

 vation of about 295 feet above Lake Michigan. The following is the 

 section developed by an examination of a series of drillings preserved 

 by Mr. Cyrus Miner, to whose kindness also I am much indebted for 

 other information relating to the Avell : 



From 1 to 100 feet, open -well through gravel. 

 From 100 to 240 feet, "rmmuig gravel." 



At 240 feet, sand and gravel of drift origin; several kinds of rook represented. 

 At 259 feet, sand, gravel and calcareous claj'. 

 From 215 to 240 feet, calcareous arenaceous clay. 



From 260 to 350 feet, sand and gravel, largely quartz and chert, a little granite, dio- 

 rite and some limestone. 



POTSDAM. 



From 350 to 360 feet, a red oclierous material mixed with a nearly equal quantity of 

 green particles much resembling the green sand of the Upper Potsdam. Drift gravel, 

 probably from above, also present. The red and green mixture effervesces tardily in 

 cold acid (hydi-ochloric), but reij briskly in hot, showing a caloai-eous and magnesian 

 element present. 



At 390 feet, hght colored quartzose and cherty sand, with a few granitic and calcare- 

 ous grains. 



At 400 feet, fine-gramed wliite, chiefly quartzose sand, but indicating the presence of 

 calcareous material by a shght effervescence with cold, and strong action with hot add. 



At 450 feet, essentially the same as above. 



At 515 feet, quartzose sand, red ocherous material, and particles of a pm-plish shaly 

 rook partially soluble in hydrocliloric acid. 



At 530 feet, reddish ocherous material, dark calcareous shale and small drift pebbles. 



At 565 feet, greenish blue calcareous shale containing niinute glistening scales re- 

 sembling mica. 



From 660 to 570 feet, similar to the last. 



At 615 feet, fine grained light yellow quartzose sand; slight effervescence. 



