FORESTRY SURVEY 185 



has denuded the surface of the more recent soil additions. 

 These clavs are, as a rule, exceedingly tenacious when 

 saturated with moisture, and almost rockdike when dry. 



Fortunately for the agriculttirist, this class of soils rep- 

 resents a yery small per cent of the whole area, and, as 

 intimated above, it is only on the more broken and steeper 

 land surfaces that the peculiar characteristics of the clays 

 are clearly pronounced. Here, almost without exception, 

 the land is devoted to woodland or pasttire or a combina- 

 tion of both, and so soil defects play very little part in the 

 calculations of the farmer. 



Loess. , 



The very large majority of Jo Daviess county soils are 

 to be classed under the very much debated name of loess, 

 which, in the language of the soil experts, signities silts or 

 silt loams. Brietly, some intelligent idea of how these soils 

 originated may be obtained from the following visualiza- 

 tion of a condition of the time dtiring or following the 

 glacial ice-caj) stage in the Mississippi valley ; a tremendous 

 melting ice-sheet to the northward, sending down by the 

 great glacial flood river, the Mississippi, immense qtianti- 

 ties of debris of every sort restilting from the ice action; 

 this flood of very variable volume, according to the inter- 

 mittent character of the melting, now extending from bluff 

 to blufl: of the ancient drainage trough, and now very 

 largely reduced, with immense flats uncovered and with- 

 out vegetable cover, subjected to the desiccation of sun 

 and wind. 



Large impounded bodies of water covered much of the 

 peneplain and of the drainage valleys, due possibly to 

 overflows from the glacial margin into and over the drift- 

 less area. Prevailing westerly winds, prestimably from 

 altered climatic conditions more continuous and intense 

 than any now existing, catching up great clouds of this 

 desiccated and minutely comminuted soil of the exposed 

 flats gradtially losing their earth burden the farther they 

 travelled away from the source of the soil, deposited a 

 horizontal soil cone. or. rather, wedge, thick near the river 

 margin and thinning to zero at an undetermined distance 

 eastward. This mantle, covering hill, valley, mound, ridge, 

 and every retaining surface and depositing in the great 

 impounded waters a similar load to be modified by water 

 action, is the "loess" of today. 



