UNION COUNTY. 331 



exposed to the air and surface water, but also with the ease with which 

 these agents find access below. A sandy or gravelly knoll is generally 

 weathered deepen than one of clay, and a rolling surface is apt to be 

 more deeply oxydated than a flat one. 



The Drift ridge which separates Big Darby and Mill Creeks has already 

 been alluded to under the head of Surface Features. Its exact form, limits, 

 and location, even within the county, have not been fully made out. The 

 time given to the county would not allow a careful survey of this ridge 

 in detail. It is well known to the inhabitants of the county. It forms 

 a belt of high and rolling clay land which shows bowlders and gravel 

 somewhat more abundantly than the surface of the rest of the county. 

 It is believed to be of the nature of a glacial moraine, and was probably 

 thrown down by the ice at a period when the retreating ice-foot was 

 nearly stationary for a long time at about that place. It is very similar 

 to those other very extended Drift moraines that cross north-western 

 Ohio, but is somewhat more clayey than they. Its connection with 

 them is not known, but it was doubtless cotemporaneous in origin with 

 one of them. The elevated region in Logan county, where there is an 

 island of Devonian rock which withstood the ice-period, was a disturbing 

 element in the otherwise very regular contour of the foot of the glacier. 

 Union county seems to have been in the pathway of a spur or branch of 

 the ice-sheet, and to have suffered very extensive erosion thereby. 

 After the actual withdrawal of the icefrom the county, the drainage of 

 a large tract of ice-covered surface would have passed principally through 

 the same pathway. This pathway is bounded on either side by a per- 

 sistent barrier of Corniferous limestone. It is probable, also, that the 

 Waverly overlay this area, at least in the- Logan county island, since 

 fragments of the Berea grit are found in the Drift in the south-western 

 part of Union county. The effect of this drainage over the county is 

 probably seen in the near approach to the surface of heavy gravel beds 

 in the Drift over wide tracts, although the level of the county in the 

 same tracts is now that of the general country, and is perfectly fiat. 

 This may be seen in the frequent gravel pits about Richwood and.Essex, 

 where the surface is outwardly comparable to that of the Black Swamp 

 of north-western Ohio, but is so closely underlain with gravel that 

 almost every cellar encounters it within three or four feet. This gravel 

 belt runs southward toward Pharisburg, and is also penetrated on the 

 farm of Mr. Josiah Westlake, a mile and a half north of Marysville, 

 who avers that small "shiner fish " appear late in the summer, or in the 

 fall of nearly every year, in a shallow well curbed by a " gum," which is 



