44 WALKS AHD TALKS. 



other lacustrine deposits attending the high water, rest on the 

 Drift. The entire broad region covered by the high water is 

 overspread by a sheet of lacustrine clays and thin seams of 

 sand. These deposits exhibit a regular horizontal stratifica- 

 tion. Occasionally we find a bowlder imbedded in them. 

 Excellent material for bricks and pottery is furnished by the 

 clays ; and in many situations, as at Milwaukee, the absence 

 of iron prevents the production of a red color in burning. 

 The famous "Milwaukee bricks" are of a pale lemon color, 

 or even, in some cases, as white as chalk. This sort of clay 

 occurs on both sides of Lake Michigan. 



These lacustrine deposits rise from the shore with the gen- 

 eral slope of the earth's surface, to the upper level reached by 

 them. The lowest beds come to the surface at the highest 

 elevation. Often these are sandy; and, becoming saturated 

 with rain at the surface, they convey a sheet of fresh water 

 under the other deposits to the lower levels. These water- 

 bearing sheets pass under the cities which have been built in 

 modern times on the lacustrine border. In some cases, as at 

 Toledo, and many points on the north shore of Lake Erie, 

 artesian borings have been carried down to the water-bearing 

 strata, and thus artesian wells have been obtained. 



We have been considering lake-terraces and high water in 

 the Great Lakes. But every observer has noticed terraces 

 also along the borders of rivers. On the lower Ohio they 

 occur up to 160 feet above low water ; at Louisville, 128 feet 

 above low water; near Cincinnati, 120 feet. On the Con- 

 necticut, they range from 150 to 240 feet above the modern 

 flood level. On the Missouri we find them up to 335 feet ; 

 on the Athabasca and Saskatchewan, up to 370 feet. There 

 is no need of citing further ; for these facts show that the 

 rivers in all the northern parts of the country have been 

 enormously flooded, as well as the lakes. These terraces, also, 

 rest on the top of the Drift deposits. The flooded waters, 

 therefore, in general, existed after the events which left the 

 Drift overspreading the northern states. 



Now let us reason a moment from the facts which have 



