334 GEOLOGY OF OHIO. 



TIMBER. 



In the broad valleys of the streams the native timber was mainly hard 

 maple and black walnut; of the latter a very large part was destroyed 

 before its value was known, but very much has been cut and shipped to 

 market. The large sugar maples in this district seemed a strange thing, 

 but the thorough drainage afforded by the deep deposit of gravel fully 

 explains their presence. If the alluvium rested upon clay, we should 

 find soft maple, elm, and sycamore growing upon it, but no sugar maple. 

 On the Waverly hills a mixed forest of maple, beech, hickory, oak, and 

 pepperidge ; in a few places on the borders of the stream hemlock, and 

 on the ridges where the Waverly Conglomerate comes to the surface, 

 chestnut. On the Coal Measure rocks the predominating timber is oak. 

 On all the hills are scattered trees of whitewood, cucumber, black and 

 white ash, and elm; the latter three being most abundant where the 

 original glacial Drift remains. 



GEOLOGICAL STRUCTUEE. 



The series of rocks exposed in the county comprise about two hundred 

 and seventy-five feet of the Coal Measures, and about three hundred feet 

 of the Upper Waverly, but borings for oil have extended our knowledge 

 of the strata down to the Huron shale, and have afforded important in- 

 formation in regard to the character and thickness of the sub-carbonifer- 

 ous rocks. 



The following is a general section of the rocks underlying Knox county, 

 as made known by observations of rock expos.ares and by the borings for 

 petroleum : 



