192 GEOLOGY OF EASTERN WISCONSIN. 



CLASS II. The Lighter Marly Clay Soils, or Clayey Loams 

 These are drift soils, having been derived chiefly from a calcareous 

 bowlder clay, which in turn was formed by the powdering of various 

 kinds of rocks, but chiefly magnesian limestones, by glacial agencies. 

 It therefore contained originally a large proportion of calcareous and 

 magnesian material, and a less amount of silicious and aluminous; 

 but the leaching action of water and the growth of vegetation has re- 

 moved a much, larger amount proportionally of the lime and magne- 

 sia than of the other ingredients, so as to leave these the chief con- 

 stituents at the surface. But the deeper subsoil is highly marly in 

 its nature. There is just enough of sandy material in it to make it 

 loamy. The dark vegetable matter does not penetrate as deeply as in 

 the prairie loam, so that the plow frequently turns up the reddish or 

 yellowish subsoil containing very little humus. This soil works with 

 the utmost facility, indeed is unsurpassed in this respect. It stands 

 both wet and drought well, and is a very durable and fertile soil. 



This class graduates into the sandy loams on the one hand, and 

 heavier clayey loams on the other. It prevails in the same general 

 region as the prairie loams, its areas being irregularly interwoven 

 with them. 



CLASS III. The Heavier Merely Clay Soils, or Heavier Clayey 

 Loams. This class is similar to the preceding, both in origin and 

 character. But the drift from which it was derived contained more 

 Archaean bowlders, especially those containing feldspar, hornblende, 

 and similar minerals in large proportion. From the powdering and 

 disintegration of these, a large amount of clay proper was derived, 

 mingled, however, with the quartzose material of the same rocks and 

 with much calcareous and magnesian clay, derived in a similar way 

 from the -dolomites which usually form a prominent part of the drift. 

 This is not then a true clay soil, for there is a notable proportion of 

 lime, magnesia and free silica present, but it is, as named above, a 

 marly clay, of the heavier class, when compared with the foregoing. 

 The term loam is not properly applicable to the subsoil, but at the 

 surface, drainage has exercised an assorting influence over it, separat- 

 ing and carrying away the finer material, and leaving the sand, which 

 gives to the surface a lighter loamy character. This surface soil 

 rarely gives any effervescence when submitted to the action of hydro- 

 chloric acid, while that from greater depths usually responds with 

 vigorous action. We find here again what I have found to be true 

 everywhere, that the surface soil is almost entirely exhausted of the 

 carbonates of lime and magnesia, even where they exist in g x eat 

 abundance in the deeper subsoil. And it is for this reason that tiie 



