228 The American Oeologist. Aprii, i89o 
little more than guess. What forms of life inhabited that sur- 
face in the earliest time the palaeontologist has not yet dis- 
covered. The land on which they once dwelt is gone and the 
marginal beds have thus far yielded no trace of any remains 
that chance may have washed into them. All is blank. 
This land area remained above the water,doubtless with great 
variation from time to time, throughout the whole palaeozoic 
era and afforded, in part at least, the material that went to 
build up the enormous sediments of middle Pennsylvania. If 
total submergence occurred it was neither long nor permanent 
and all evidence of it fails. Successive maps, could they be 
constructed, would show much change of detail but the Pal- 
£eozoic Coast Survey has not yet begun its labor, has not indeed 
been appointed and it would be foreign to our porpose to en- 
cumber this sketch with minute and speculative details. 
The Ordovician (Lower Silurian) era passed away with all 
its minor divisions of Calciferous,Chazy, Trenton and Hudson 
River groups and at its close there was a prophetic manifesta- 
tion of Earth-force which outside of Pennsylvania forced up the 
newly deposited strata in western Ohio into a wide anticline ex- 
tending from southwest Ontario to Tennessee now known as 
the Cincinnati arch. Rising above water it formed an island 
in the palaeozoic sea which existed for a long time, till sharing 
in the general subsidence it ultimately sank and was covered 
with the later deposits of Silurian and Devonian sediments.^ 
Though it is usually considered that this manifestation of 
Earth- force failed to leave any discoverable impress on the 
geology of Pennsylvania yet it is somewhat doubtful if this 
opinion is well founded. Certain signs in the southeastern 
part of the state betray at the close of Ordovician time an 
epoch of disturbance of considerable extent and importance. 
A glance at the map shows that these rocks extend much 
farther in that direction than do any of the succeeding palaeozo- 
ic strata. Though the exact age of the great limestone rang- 
ing through York, Lancaster and Chester counties is some- 
what uncertain, yet there can be no reasonable doubt that it is 
^It must not be inferred from this general remark that this submer- 
gence was continuous. Probably the Cincinnati Island existed inter- 
mittently during the whole later palaeozoic era. At times it was cov- 
ered with water and at others dry. In the Hamilton period for ex- 
ample it was probably dry while in Corniferous and Huron ages it was 
apparently subm^erged. 
