274 GEOLOGY OF OHIO. 



Soil and Timber. — The soil generally is dependent on the nature of the 

 northern Drift. In this the various essentials, such as iron, lime, phos- 

 phorus, silica, magnesia, alumina, and soda, are so thoroughly mixed and 

 in so favorable proportions that the strength and fertility of the soil are 

 very great. The depth of the soil has the same limit as the Drift itself, 

 which is, on an average, about twenty-five feet. The soil is more gravelly 

 and stony in the rolling tracts. The stones come partly from the under- 

 lying rock, but mainly from the Drift. They are common along all the 

 valleys of streams and creeks and in shallow ravines. They are made 

 to appear superficial by the washing away of the clayey parts of the Drift, 

 and are not due to any Drift agency acting since the deposition of the 

 great mass. The north-western part of the county has a heavy clayey 

 soil, with some exceptions. This clayey, flat land is comparatively free 

 from superficial bowlders. Very little gravel can be found except in the 

 line of gravel knolls that passes north-westwardly through Radnor town- 

 ship. The valleys of the streams, however, show a great many northern 

 bowlders, as in other parts of the county. Besides these general charac- 

 ters of the soil of the county, a great many modifications due to local 

 causes will be seen in passing over the county. There are some marshy 

 accumulations, which, when duly drained, are found to possess a soil of 

 remarkable ammoniacal qualities, due to decaying vegetation. The 

 alluvial river margins possess a characteristic soil, strongly contrasting 

 with the generally clayey lands of the county. They are lighter and 

 warmer, while they are annually renewed, like the countries of lower 

 Egypt, by the muddy waters of spring freshets, and are hence of ex- 

 haustless fertility. 



The whole county was originally wooded with deciduous trees, which 

 were associated, in the eastern portion, with a few species of conifers. 

 Rev. J. H Creighton, of Delaware, has kindly furnished the following 

 list of 



Trees, Shrubs, and Woody Vines Found Growing in Delaware County. 



Abies Canadensis Michx. Betula nigra...! L. 



Acer saccharinum Wang. Bignonia capreolata L. 



" rubrum L. Crataegus cordata Ait. 



" dasycarpum Ehr. " oxycantha L. 



Ampelopsis quinquefolia Michx. " coccinea L. 



Alnusincana Willd. " flava Ait. 



Amelanchier Canadensis Torr&Gr. Cornus florida L. 



Asimina triloba Dunal. " Canadensis L. 



Aesculus glabra Willd. " paniculata L'Her. 



Benzoin odoriferum Nees. " alternifolia L. 



Betula papyracea Ait. (?) Carya alba Nutt. 



