PAPERS ON BIOLOGY AND AGRICULTURE 155 



limestone as a rock wall, this last being dull gray to cream 

 color, coarse-grained and porous. It is the Galena lime- 

 stone that forms the bluff at Pine Creek upon which grows 

 a stand of white pine. The above limestones, belonging to 

 the Trenton group, are sometimes referred to as the Tren- 

 ton-Galena limestones. 



The Rock, on the whole, may be considered as, even in 

 the preglacial beds, an immature postglacial river, since 

 some erosion has taken place since the glacial period. Con- 

 sidered thus it is in the second phase of river development, 

 that of bluffs, with erosional and depositional banks at vari- 

 ous places. In this mid-phase of river development there 

 frequently occurs an overlapping of bluff and flood-plain, 

 and this is seen in the Rock. It should be noted, too, that 

 much of the flood-plain development is artificial in nature, 

 due to the formation of sand and gravel bars after the 

 breakage of dams, as at Oregon and Grand Detour. 



It will be seen that the region is one altogether of the 

 varied physiography of a river in its mid-phases with an ac- 

 centuation of the topography in many places owing to the 

 older preglacial parts. The soils belong to the following 

 classes of the five recognized by the State Soil Survey. Up- 

 land timber soils, the yellow to yellow-gray loams. Residual 

 soils, including stony loam and rock outcrop. Terrace soils, 

 which include bench lands (second bottom lands, formed by 

 deposition from overloaded streams during the melting of 

 the glaciers). Bottomland soils, which include the overflow 

 lands or present flood plains along streams, and other poorly 

 drained lands. The last class includes swamp soils else- 

 where in the state. There are, however, no swamps in Ogle 

 County. The remaining soil class, outside of the region es- 

 pecially under consideration in this paper, is that of the up- 

 land prairie soils, in the main the brown loams. These are 

 rich in organic matter and are said to have been covered 

 originally with prairie grasses, whose partly decayed roots 

 have been the source of the humus. The upland timber 

 soils are said to include practically all of the upland that 

 was formerly covered with forests. The question raised 

 thus, as to whether the vegetation caused these soils to be- 



