SURFACE GEOLOGY. 663 



SURFACE GEOLOGY. 



Soil and Subsoil. The quality of the soil of the Lead region is 

 chiefly dependent on the character of the subjacent formations. The 

 subsoil appears to be derived directly from the decay and disintegra- 

 tion of the strata, of which it is the residuum. South of the princi- 

 pal watershed, the subsoil is clay, almost without exception, having 

 a thickness of from three to six feet, depending on the configuration 

 of the underlying rock formation. This is the average thickness, on 

 comparatively level land; on side hills it is usually much thinner, the 

 greater part having been washed down into the valley below. The 

 clay soils and subsoils appear to consist chiefly of those portions of 

 the overlying Galena limestone, and earthy Cincinnati shales, which 

 being insoluble in water, were not removed by the gradual process of 

 denunation. 



The amount of lime, magnesia, and alkaline earths in the subsoil 

 and soil, together with the vegetable mold in the latter, constitute a 

 soil, which, in its virgin state, is unsurpassed for richness and fertil- 

 ity. The number of successive wheat crops which have been raised, 

 without regard to rotation, on some of our prairie farms, attest its 

 native strength; as also the marked decline in fertility of the soil 

 when this has been done, shows the inevitable retribution which fol- 

 lows the practice. 



Exceptions to the clay soil, usually found in the country covered 

 by the Galena limestone, are found in the eastern part of La Fayette, 

 and frequently in Green county, where the soil is quite sandy, owing 

 to the disintegration of calcareous sand layers frequently found there 

 in that formation. A few localities are cited below, where the sand 

 was so abundant, that the formation might have been considered a 

 sandstone, were it not for the occasional outcrops of Galena limestone 

 in place. In the western part of the town of Jordan, T. 2, E. 6 E., 

 in sees. 2, 11 and 14, the ridges have a great deal of sand contained 

 in the soil. The roads are frequently sandy, similar to those in a 

 sandstone formation. Lying entirely without the limits of the Drift, 

 this circumstance led to a search for and discovery of the original 

 beds. 



At the village of Martin, in the S. E. qr. of sec. 32, T. 1, E. 6 E., 

 on the Fecatonica river, at the saw-mill, is a large stone quarry, of 

 which the upper portion consists of Galena limestone in thin beds, 

 containing considerable calcareous sand between the layers. This is 

 the first locality where the sand was found in place. 



On the ridge near the quarter-post of 29 and 32, T. 2, E. 6 E., a 



