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is necessary to obtain a reasonable conception of these elemen- 

 tary factors in distribution. No region of Illinois probably 

 compares to Jo Daviess county in the extent and perfection 

 of the drainage elements, for it must be remembered that we 

 are dealing with an ancient land surface that for milleniums 

 has been subjected to the erosive action of frost and rain, so 

 far as we know, without a break since the days of the Niagara 

 limestone. Countless ravines and small and large valleys cut 

 up the surface in every directon, so that a plot of level land 

 is a rarity, every where slopes, more or less pronounced, being 

 the topographical feature paramount in the landscape. Only 

 on the expanded summits of the watersheds are there any areas 

 of poor drainage found and these are of limited extent, and yet, 

 as shown hereafter, they are sufficiently potent to produce a 

 forest association. The water table is in many parts very deep 

 in the earth, this being practically true of large portions of the 

 Galena limestone, and yet only on very limited and very local 

 land surfaces is a genuine scarcity of water to be found. As 

 the rainfall is about forty inches per annum, plant life rarely 

 suffers any serious drawback from this source. The soil is 

 everywhere the result of disintegrated rock remaining in situ 

 except on the "bottoms" of the streams, small and large, where 

 considerable areas of alluvium are found, and again some more 

 or less pronounced loess soils, particularly in evidence in some 

 of the area bordering the Mississippi river (see Soil Survey 

 of the Dubuque Area). A clay subsoil, grayish, yellow, or 

 even ocher red, with a few flints here and there, of many feet 

 thickness, merges into a surface soil of clay, clay-loam, or even 

 a black humus in limited districts, the latter particularly in 

 evidence as border deposits where the forest and prairie join, 

 or at the junction of Niagara and Cincinnati shales. A very 

 limited amount of sand is found in these soils, but near the 

 Mississippi river are several square miles of sandy soils of 

 varying purity, evidently of river and wind formation. 



Owing to the general uniformity and topography, we find 



