LACUSTRINE CLAYS -BOG IRON ORES. 635 



(4.) The stratified drift of the valleys owes its structure and distri-^ 

 lution to' the water of the swollen streams and lakes that marked the 

 time of melting of the glaciers. 



(5.) The depth helow the present surfaces of the rock valleys ap- 

 pears to indicate a greater altitude of this part of the continent, du- 

 ring the Glacial period, than at the present time. 



LACUSTRINE CLAYS. 



lilxteiiTliBg niland from Lakes Michigan and Superior for many 

 miles, and reaching elevations of several hundred feet above the lakes^ 

 are stratified beds of loose material, chiefly marly claj's, with more 

 or less sand, some gravel and a few bowlders. These are proved to 

 be, with but little doubt, of lacustrine origin, by the manner in which 

 they follow the shores of the lakes, and they register a depression of 

 several hundred feet, corresponding to the period subsequent to the 

 melting of the glaciers, when all the lakes and streams of the north- 

 ern part of the United States were greatly expanded beyond their 

 present limits, and the whole northern part of the continent stood at 

 a lower level. 



In the Central Wisconsin district the lacustrine clays have only a 

 small development, most of the district being either too high to have 

 been reached by the lake depositions, or else lying behind the divid- 

 ing ridges. The eastern towns of Waushara county, however, are 

 underlaid by a considerable thickness of red clay belonging to this 

 formation. The surface elevation of the country here is 160 to 20O 

 feet above Lake Michigan, and the clays 80 to 100 feet and over in 

 depth, as shown by numerous Artesian well borings that yield a flow 

 of water which is obtained from seams of gravel at different horizons 

 in the clay. The clay of eastern Waushara county is part of a large 

 clay area that extends up the Green Bay valley from Lake Michigan. 



BOG IRON ORES. 



' The most recent formations of the Central Wisconsin district are 

 the marsh deposits of peat and bog iron ore. The latter is found on 

 a small scale underlying the peat of many marshes, and also occur- 

 ring at points not now marshes, but still showing signs of a marsh 

 origin. The large marshes of Juneau, Wood and Portage counties 

 have yielded the best indications of the existence of good bog ore, 

 although the points at which any quantity can be seen are few in 



number. 



At Necedah, Juneau county, immediately south of an isolated 

 hill of Arehffian quartzite, is a tongue of the great marsh that 



