130 IOWA DEPARTMENT OF AGRICULTURE. 



spicuous recessional moraines; and so areas of knobby drift of considerable 

 extent are distributed in the Wisconsin area at varying distances from the 

 outermost margin. Recessional moraines are especially well developed in 

 Palo Alto, Emmet and Dickinson counties. 



Intimately related to the subject of Wisconsin moraines are the many 

 charming lakes of Iowa. There are no lakes worthy of note in the Kansan, 

 Illinoian or lowan areas. All our lakes are of Wisconsin age, and most of 

 them occupy basins in the irregularly piled morainic ridges. Indeed it was 

 the very lawlessness accompanying the deposition of the morainic materials 

 that left the enclosed basins in which imprisoned waters might accumulate. 

 Clear Lake lies in such a basin in the eastern moraine, surrounded by promi- 

 nent constructional hills and knobg. Spirit Lake, the Okobojis and a num- 

 ber of beautiful but less important sheets of water in the same part of the 

 state, are all located in an extensive morainic belt belonging to the reces- 

 sional series. The beauty and charm of all these delightful bodies of water 

 are greatly enhanced by the eccentricities of distribution, and the ever vary- 

 ing curves and slopes and outlines, of the surrounding morainic knobs. 



Among the interesting, though rather inconspicuous topographic fea- 

 tures of the lake region are the walls, embankments and causeways which 

 coincide in position and direction with lake margins, and often present the 

 deceptive appearance of railway grades or other artificial structures. So 

 common are these that they may be expected to occur somewhere, in some 

 form, along the margin of every considerable sheet of water in northern 

 Iowa. The conspicuous ridge of sand, gravel and bowlders lying along the 

 lake shore in front of the Assembly grounds at Clear lake, must be familiar 

 to every visitor. When this marginal feature of our northern lakes assumes 

 the form of a rude wall of cobbles and bowlders, it seems to be capable of 

 taking a stronger hold on popular attention and popular imagination. 

 Hence it is that our Walled Lakes have long been famous, descriptions of 

 them occupying column after column in newspaper and magazine, while 

 other lakes bordered by embankments of plain sand and clay, though 

 equally as interesting and instructive, equally as worthy of investigation 

 and comment, have suffered the neglect and inattention that usually falls to 

 modest, unobtrusive merit. 



These marginal ridges and walls, along the shores of northern lakes with 

 shallow basins, have been heaped up by the expansion of ice in winter. In 

 our severe climate, particularly if the snowfall be not great, quite an ex- 

 tent of shoal water near the shore freezes to the bottom . Indeed the effects 

 of freezing go deeper than the water, and bottom sands and clays and bowl- 

 ders become a part of the frozen sheet. The alternations of temperature, 

 such as take place between colder and warmer days or between noon and 

 midnight, affect the volume of the ice in such wise that from day to day 

 it expands and is thrust shoreward with tremendous energy. The resist- 

 ance is least on the low, gradually sloping shores, and here the move- 

 ments are most pronounced. The marginal ice, with all the materials 

 frozen in its lower surface, is shoved up on the slope, and stones and 

 earth are left as a contribution to the growing ridge or wall when melting 

 takes place in the following spring. The process has been going on for cen- 

 turies, and where the conditions have been most favorable, the results are 

 somev/hat surprising. 



