188 ILLINOIS ACADEMY OP SCIENCE 



D, Brown Silt Loam. — The brown silt loam forms a 

 fringe along the northeast and east margins of the region, 

 narrowing to the west and south. It reaches a maximum 

 width of three miles in northeastern Jo Daviess county, 

 but extends for a number of miles into Stephenson county 

 to the east and Wisconsin to the north. This soil is very 

 dark by reason of its humus content and is highly fertile 

 and almost coextensive with the drift, extending, however, 

 on an average about two miles beyond the western margin 

 of the same. The portion adjacent to the drift appears to 

 have been always prairie while that portion adjacent to 

 the yellow silt loam has been invaded by forest. 



Ey Black Silt Loam. — (Lintonia loam of the Dubuque 

 soil survey.) This is the fringe of alluvium along all of 

 the more important streams, varying from zero to a mile or 

 more in width. Always black in color and of high fertility, 

 this soil was originally either occupied by a heavy growth 

 of timber or by curious narrow strips of marsh grass, re- 

 sembling small prairie areas. These grasses usually occu- 

 pied the very wet portions of the alluvium, and almost 

 invariably indicated a spring or water seepage. Agricul- 

 turally this soil is the most fertile of any, but is subject 

 always to the menace of floods. 



F^ Rock Soil; G, Sand; II, Black Muck. — A brief para- 

 graph will dispose of the soils above named. The rock soil 

 (F) is represented by the outcrops of the Niagara and 

 Galena limestone. These have a vertical separation of a 

 hundred feet or more occupied by the shales of the Maquo- 

 keta formation which do not outcrop at any point. Sands 

 and sandy loams (G) are found only in the terraces of the 

 Mississippi Eiver and on the adjacent bluff crown. They are 

 particularly developed in the sand prairie, a strip from 

 one-half to two miles wide and fifteen or more miles long 

 occupying the southwest border of the county and present- 

 ing in almost every feature the aspect of the arid western 

 plains. These soils are coarse or fine in texture, according 

 to their position, and are plainly river or dune formations. 

 The hlack muck (H) soil is very limited in extent, and 

 appears only in the bottom-lands, here and there, as un- 

 drained areas or as "quaking bogs" of limited extent and 

 curious physical structure. The former are usually heav- 

 ily wooded ; the latter, never wooded. 



