Devonian Era in the Ohio Basin. — Claypole. $7 
many-colored shales through which the auger descends in 
search of gas or oil or salt. It is consequently impossible to 
show its extent over the state or to map the exact minimum 
area of the Hamilton sea in Ohio. By indirect evidence, how- 
ever, it is possible to indicate the larger details of the geography - 
of the period in the gulf of Appalachia with considerable ac- 
curacy, and thus to see its connection with that of the pre- 
ceding periods. 
The general outline of the western part of the Appalachian 
gulf differed from that represented in the map of the preceding 
Corniferous-Hamilton period. The wide opening around the 
north end of the promontory of Cincinnati still maintained 
communication with the open western ocean and a shore line 
extended along the western side of the arch to the site of the 
present falls of the Ohio, where, as above shown, the upper 
beds have a strong Hamilton affinity. Turning to the east- 
word, the coast-line swept inward, for the most part coinciding 
or nearly coinciding with that of the preceding period. The 
absence or non-recognition of the true Hamilton in the out- 
crops of central and southern Ohio may, if not resulting from 
defective evidence, indicate that the land there was somewhat 
more extensive than previously — a consequence, probably, of 
the continued elevation of the Cincinnati arch. Eastward, how- 
ever, the reverse of this condition prevailed and throughout 
middle and eastern Pennsylvania the Hamilton waters over- 
flowed the former shore lines and converted into sea what had 
before been dry land. In that region, where, as already point- 
ed out, the Corniferous limestone is largely missing, the thick 
beds of the Hamilton rest on the Oriskany or on the Lower 
Helderberg directly. There, also, the formation attains its max- 
imum thickness of 1500 feet. What additional area to the 
southeast should be added to allow for the crumpling, folding 
and erosion that have since then taken place it is not possible to 
say, but beyond question the Hamilton shore-line lay many 
miles beyond the extreme outcrop of the Hamilton strata. 
Sweeping northward through New Jersey and New York 
to the Hudson river near Albany the outcrop of the Hamilton 
turns thence to the west and passes below lake Erie at Buffalo. 
Reappearing on the north shore it runs northward and divides, 
one branch passing under lake Huron, across Michigan and 
