SOILS, ETC. 125 



Nishnabotany sandstone exists, close observation shows 

 the soil to contain more sand in its composition than else- 

 where; yet it is never sufficient in amount, even there, to cause 

 it to approach barrenness. On the contrary, it adds a 

 warmth and mellowness to the soil which are beneficial. The 

 same may be said of the soil of some parts of the State 

 occupied by the Lower coal-measures, the sandstones and 

 sandy shales of that formation furnishing the sand. 



In northern and northwestern Iowa the drift contains a 

 greater portion of sand and gravel than elsewhere; conse- 

 quently the soil also partakes of the same composition, but 

 yet even there the barren spots are rare exceptions to the 

 general fertility, because the proportion of coarse material is 

 greater beneath than upon the surface. The sand and gravel 

 of this region was doubtless derived from the Cretaceous 

 rocks, that now does or formerly did exist there, and also in 

 part from the conglomerate and pudding-stone beds of the 

 Sioux quartzite. 



Again, in some parts, as for example, in southern Iowa, the 

 soil is frequently stiff and clayey, but very fertile. The 

 subsoil, together with the whole thickness of the drift, is also 

 clayey. This preponderating clay is doubtless derived from 

 the clayey and shaly beds which alternate with the limestones 

 of that region. It must not be understood, however, that clay 

 is anywhere absent from the drift soil, not even from that of 

 those parts where the underlying rocks contain only a minute 

 proportion of clay ; for, as before stated, much of the fine 

 material of the drift, and consequently of its soil also, had 

 its origin to the northward — some of it being derived from the 

 granitic rocks there which contain, in large proportion, the 

 necessary material for the production of clay. 



The origin of clay and of soil from such rocks, when 

 decomposed, may be finely illustrated by taking a handful of 

 the decomposed granite from the valley of the Redwood 

 before referred to, and stirring it up thoroughly in a vessel of 

 water. The fine grains of quartz it contains disseminated 

 throughout the mass become at once precipitated to the 



