PREBLE COUNTY. 405 



An examination of these altitudes, in connection with the appended 

 map of the county, will serve to show that, in a general way, they con- 

 siect themselves directly with the geological formations. In other words, 

 a geological and a topographical map of Preble county will have many 

 points in common. The Cliff Limestone may be said to have an altitude 

 ■of more than five hundred feet above low-water at Cincinnati, and the 

 Blue Limestone an altitude of less than five hundred feet. Elevations 

 No. 4 and No. 6, above given, show exceptional altitudes for the 'B]jie 

 Limestone, and are to be explained, at least in No. 4, by the presence of 

 heavy beds of drift. 



The drainajge of the county is prisicipaily effected by four streams, 

 named in the order of their importance, Twin Creek, Seven Mile Creek, 

 Four Mile Creek, and Elk Creek. All of these deliver water to the Oreat 

 Miami. On the extreme western boundary, small areas are found, the 

 drainage of whi«h is directed to White River. The highest land of the 

 county is found on the dividing ridge between these drainage basins, the 

 water-shed passing through Israel, Dixon, Jackson, Jefferson, and Mon- 

 roe townships. 



Parts of Washington and Jackson townships lie quite flat ; but there 

 are no swamps in the county, and no considerable areas from which the 

 water runs even sluggishly. The Blue Limestone corner of the county, 

 comprising Twin, Lanier, Gratis, Somers, and<3rasper townships, is beauti- 

 fully diversified in surfece, and constitutes a very attractive as well as a 

 'yery rich agricultural district. 



©EOLOGICAI. SEMBB. 



The geology of the county agrees very closely, as far as its bedded rocks 

 are concerned, with that of Montgomery county and Clarke county 

 already reported upon. It will not, therefore, need extended treatment 

 liere. The series comprises three main elements, one of which belongs 

 to Lower Silurian time, while the other two are of Upper Silurian age. 

 The series can be shown in diagram thus : 



Upper SiluTLao. 



Niagara Ctroup. 



Gnelp?!. 



SpriugfieM stona. 



Niagara shales. 



Dayton etone. 

 Clinton Lim«8tone 



Lower SLlarkiii ^ Cincinnati Group, Lebanon division. 



The approximate thickness of the divisions can be given as follows: 



PEET. 



Kiagara Gronp ..- • 75 



Clinton Limestone .„ - 15 



OincimuitifrCdnp. ...... ...-...■. ................ .......... 225 



