656 GEOLOGY OF OHIO. 



quent in those parts of south-western Ohio that hold the southern edges 

 of the true Drift. Ross County is no exception to this statement, but it 

 must be added that there have nowhere within its limits been found such 

 districts as those around Marshall and New Market, Highland county, in 

 which almost every well strikes into buried vegetation. 



V. DIP OF THE STRATA. 



In concluding the discussion of this general area, a few facts will be 

 given touching the dip of the strata that have now been described. The 

 appended map, which takes in Highland, Pike, and Ross counties, fur- 

 nishes the necessary data for determining approximately the amount and 

 general direction of the inclination of the bedded rocks that underlie 

 this district. The following pomts are used in this determination: 



Near the village of Samantha, five miles north of Hillsborough, the 

 westernmost outlier of the Huron shales, or great black slate, is found. 

 The line of junction between the limestones and the shales is perfectly 

 distinct, and its altitude above tide-water has been ascertained. This 

 point constitutes an initial fetation, and dotted lines are drawn from it 

 to various localities, the altitudes of which above the sea are also known, 

 where the same geological boundary is shown, or where other horizons 

 that stand in a known relation to this one are to be seen. We find thus 

 five main lines along which the dip can be calculated, ranging from east 

 32° north to east 40° south. 



The first of these lines is drawn from the initial station to a point in 

 Ross county nearly opposite to Greenfield, a distance of fourteen and 

 three-eighths miles. Its course is east 32° north. The fall of the lime- 

 stone surface in that direction and that distance is two hundred and 

 eight feet, which indicates an average dip of fourteen and a half feet to 

 the mile. 



The next line extends from Samantha to Chillicothe, a distance of 

 thirty-three and three-fourths miles, in a direction 9° north of east. The 

 junction of the limestone and shales has now been carried below the sur- 

 face, but as the average thickness of the slates is known, it is possible to 

 make their upper surface a basis for calculation. Allowing three hun- 

 dred feet for the average thickness of this formation, the descent of the 

 limestone in these thirty-three and three-fourths miles is found to be 

 eight hundred and eighteen feet, or an average dip in this direction of 

 twenty-four and one-half feet to the mile. Assuming the maximum 

 thickness obtained from the shales, viz., three hundred and thirty-two 

 feet, the dip would be increased by one foot — giving as the result twenty- 

 five and one-half fe«t to the mile. 



