70 
THE FERN FORESTS OF 
form its centre and summit. This accounts for 
the great profusion of Silurian organic remains 
in that neighborhood. Indeed, there is no local- 
ity which forces upon the observer more strongly 
the conviction of the profusion and richness of 
the early creation. One may actually collect the 
remains of Silurian Shells and Crustacea by cart- 
loads around the city of Cincinnati. A natural- 
ist would find it difficult to gather, along any 
modern sea-shore, even on tropical coasts, where 
marine life is more abundant than elsewhere, so 
rich a harvest, in the same time, as he will bring 
home from an hour’s ramble in the environs of 
that city. 
These elevations naturally gave rise to depres- 
sions between themselves and the land on either 
side of them, and caused also so many counter- 
slopes dipping toward the uniform southern slope 
already formed at the north. Thus between the 
several new upheavals, as well as between them 
all and the land to the north of them, wide ba- 
sins or troughs were formed, enclosed on the 
south, west, and east by low hills, (for these more 
recent eruptions were, like all the early upheav- 
als, insignificant in height,) and bounded on 
the north by the more ancient shores of the pre- 
ceding ages. 
These were the inland seas of the Carbonifer- 
ous period. Here, again, we must infer the sue- 
