28 THE LEWIS BROOKS MUSEUM. 



Chemical Geology teaches the mode of alteration of mine- 

 rals and rocks, and the character of the products formed. 

 All soils are formed by the disintegration and decomposition 

 of rocks. No farmer need be told that the physical charac- 

 ter and chemical composition of his soil are most important 

 features in determining the amount and kind of crop which 

 he can secure. All these points are learnt from Geology. 



The topography, too, of the country influences greatly 

 the agriculture of a district. The topography results di- 

 rectly from the structure, composition, mode of decay, and 

 removal of rocks and soils. These are all geological data. 

 The presence of springs, the flow of streams, the rain fall, 

 and many other features which determine the agricultural 

 character of a country, all depend upon the geological 

 structure. Every practical farmer recognizes the differ- 

 ences in soils caused by geological differences, although he 

 may do this only from the teachings of experience. 



He knows that in this State the lands of the Tidewater 

 region differ from those of the Piedmont district, and these 

 again from those of the Great Valley or of the mountains. 

 The Geologist will tell him that such differences are caused 

 by the fact their soils are the products of rocks differing in 

 composition, in structure, and in the topography resulting 

 from their decay and erosion. Let us take an example to 

 illustrate the difference between the knowledge of the man 

 who farms by experience and that of the scientific farmer. 



There are sandstones and shales in this State which 

 contain no elements of fertility in their composition. Soils 

 made by their decay look well and yield a return, so long 

 as they contain fertilizing matter obtained from some other 

 source than decaying rocks. They cannot be permanently 

 improved, for by resting and lying fallow, they gain noth- 

 ing from the decay of the rocks, the parents of the soil. 



The non-scientific farmer could learn their true charac- 

 ter only by a long source of cultivation. But the geological 

 farmer might decide from an inspection of the rocks that he 



