PUBLIC PARKS OF IOWA 169 



drainage stream of the subsequent interglacial stage followed the old 

 depression and in part re-excavated the valley. At the beginning of the 

 lowan stage the re-excavation was far from complete, its amount being 

 represented by the space between the south wall of the valley and the 

 first terrace north of the present stream. The lowan glaciers deposited 

 only a very thin sheet of drift over this region, but they carried numerous 

 boulders that are scattered over the whole surface of highlands and lower 

 plains. The plain between the terrace and the channel, and rising only 

 a few feet above the level of the water, is thickly strewn with large 

 lowan boulders that have not been disturbed since they were deposited 

 at the level on which they now lie. The present channel is a shallow trough 

 cut in the lowan drift of this lower plain, and represents the inconsider- 

 able amount of erosion since the withdrawal of the lowan ice. 



The same history is recorded throughout the whole course of the 

 stream in the lowan drift area, except that during the interglacial stage, 

 between the Kansan and lowan glacial periods, the stream, for a few 

 miles, was turned aside from the ancient valley and expended its energies 

 in cutting the abandoned, rock-walled channel, already noted, that tra 

 verses sections 34 and 35 Lime Creek township, and a part of section 2 of 

 Mason City. The evidence of the interglacial age of this abandoned chan- 

 nel has been given in connection with the discussion of the topography 

 of the region. 



It seems probable that during the preglacial and interglacial times the 

 valley of Lime creek accomodated one of the most important streams of 

 northeastern Iowa. After the close of the lowan stage the Shell Rock 

 river probably took part of the drainage waters that had previously found 

 their way through various tributaries into the predecessor of Lime creek. 

 At all events there was no pre-Iowan Shell Rock, for this stream follows 

 no valley, and has cut only a shallow trough in the surface of the lowan 

 drift. Furthermore, the Wisconsin drift, particularly the Altamont 

 moraine, choked up that portion of Lime creek valley which doubtless 

 was produced northwestward from the point at which it crosses the north- 

 ern boundary of Cerro Gordo county. As a consequence, the surface 

 waters have been partly turned into new courses, while those that still 

 find their way from the Wisconsin drift area into the old valley are 

 obliged to wander tortuously among morainic knobs, and over areas in 

 which drainage channels are altogether undeveloped. As a result of 

 these changes the relative importance of the stream following this old 

 valley has been greatly diminished. 



The Altaimont moraine, occupying the western townships of Cerro 

 Gordo county, is an area that is practically undrained. Lime creek, 

 as already stated, flows throughout the northwest corner of Grant town- 

 ship, but it occupies the only definitely marked stream channel in the 

 morainic belt north of Clear Lake. In this region Lhne creek has no 

 tributaries except so far as the debouching sloughs and marshes afford 

 opportunity for drainage of the adjacent areas. For many miles south 

 of Clear lake there are no drainage channels, except broad swales that 



