190 GEOLOGY OF EASTERN WISCONSIN. 



cal relations of the subject are apparent. It will be sufficient here, 

 however, to call attention to the four general classes of rocks that 

 have chiefly entered into the formation of the soils of the part of the 

 state under consideration, and for fuller knowledge, refer the reader 

 to the general report. These are (1) the Archaean rocks, whose min- 

 eral nature is very complex, but which give rise chiefly to silicious 

 and aluminous material; (2) the sandstones that contribute silica; (3) 

 the shales, that are chiefly aluminous; and (4), most abundant and 

 important of all, the dolomites or magnesia,n limestones, that contrib- 

 ute lime and magnesia. Soda, potash, phosphorus, and other ingre- 

 dients, exist in small quantities in the several formations. The lime 

 and magnesia occur chiefly in the form of carbonates, and their pres- 

 ence is manifested by effervescence on the application of acid, with 

 which the soils were extensively tested in the field. 



The following descriptions of the soils of the district under con- 

 sideration relate rather to the subsoil than the soil proper; at least 

 there has been an effort to set aside purely surface characters, first, 

 because the surface soil is subject to so many local and changeable 

 influences, and has been so much modified by cultivation and other 

 artificial causes, that a series of observations upon typical or "virgin " 

 soils was scarcely possible, and secondly, because the future of our 

 agriculture depends not so much upon the present soil as upon the 

 subsoil, since winds, waters and cropping are rapidly sweeping the 

 surface away, and but comparatively few years will pass before our 

 present subsoil will be at the surface, and for the further reason that 

 the power of the surface soil to retain the strength it has, and to draw 

 mineral resources from below, is most evidently dependent on the 

 subsoil. 



If, in reading the descriptions that follow, the reader will be kind 

 enough to place before him Plate III of the accompanying atlas, the 

 areas occupied by each class will be seen more definitely than they 

 could be presented by description, which will then be for the greater 

 part omitted. It will be readily understood by every one, that soils 

 vary much in every section, and even on the, same farm, and that the 

 varieties graduate into each other in the most intricate and impercep- 

 tible manner, and yet at the same time every region has a prevailing 

 character that can be classed, described and mapped. The accom- 

 panying map is only intended to indicate such prevailing kinds, and 

 of course each color covers patches of greater or less size, of different 

 kinds. 



Notwithstanding the impracticability of mapping these local varia- 

 tions and intermediate varieties, it is believed that the map given will 



