Art. II.] BrOwnocker, Cofitferous Rocks of Oho' 13 
AREA OF EACH REGION. 
The central embraces by far the greater area. This is 
about 150 miles in length from its southern termination in Pick- 
away county north to Kelley’s Island. Its average width is 
about 12 miles, the maximum 18 miles, and the minimum about 
'5 and one-half-miles. 
The 'northwestern area has a length of over 80 miles, an 
average width of perhaps 8 miles, a maximum of 13 miles, and 
a minimum of 3 miles. 
The western area is roughly circular in shape. It is chief- 
ly a narrow belt having a width usually of about i mile, but this 
increases in one locality to 6 miles. 
STRATIGRAPHICAL RELATIONS. 
The strata in the central part of the state may be divided 
into two horizons, (i) the Lower and (2) the Upper. The two 
horizons are separated by a persistent layer of fish remains a 
few inches in thickness and known as the bone-bed. The Lower 
beds are shown at every locality examined in central Ohio ex- 
cept Delaware and Sandusky. They are frequently called the 
Columbus beds. The Upper beds are found well developed at 
Delaware, Marion and Sandusky. Between Delaware and 
Columbus, in the observed exposures, this division is represent- 
ed by shales only. It has not been found at all south of Co- 
lumbus. The division is inconstant. Sometimes it is a forma- 
tion of importance ; at other times a few feet of shales only or, 
again, it may be absent altogether. These two divisions of the 
Corniferous differ in fauna, color, and chemical constitution. 
The dip of the central division is to the southeast. At 
Columbus this is 30 feet per mile. Farther north the rate 
probably decreases as does that of the underlying formations. 
In some quarries the dip varies greatly. In Evans’ quarry at 
Marion the beds in the two ends of the quarry dip in opposite 
directions, that is toward each other. A similar state is found 
at Kelley’s Island. At White House the general dip is to the 
west, but there are many minor variations. In fact the expos- 
