April, 191 L] 
The Ancient Vegetation of Ohio. 
3 1 5 
Thus the Lower Silurian or Ordovician system includes the 
lowest of Ohio’s stratified and fossiliferous rocks, the Trenton 
limestone and the several formations of the Hudson River group. 
They suggest that a broad but shallow arm of an ancient ocean 
then covered Ohio. (5). As in the following geologic periods, the 
sediments were derived from the various rocks carbonated, oxi- 
dized, and exposed to erosion and solution, the beds of limestone 
representing for the most part an accumulation of comminuted 
particles of shells and lime-secreting plants in a clear sea, and the 
shales representing the deposits of mud made in still water nearer 
the land. The adjacent lands were probably too low or too far 
away to yield abundant sand or permit wave-action sufficiently 
vigorous to keep the mud from settling. Comparatively very few 
fossil plants of Ohio have been obtained from the geological 
formations of this period (17) ; but the records of the life of the era 
in the United States and in Europe though meager, are sufficient 
to indicate that development of life was well advanced long before 
the known strata were deposited, and that less diversity of climate 
existed than now. The testimony of the ancient organisms 
implies nearly uniform soil conditions. The plant forms, which 
in such rocks must necessarily be rare as fossils, were relatively 
simple, living along the shore and in open water in definite zones, 
and appear to have varied with the nature and the slope of the 
bottom, the depth and clearness of water, etc., much as it is 
today. Immense quantities of microscopic unicellular plants 
were undoubtedly present as plankton in the protected bays with 
sandy and muddy bottoms to form the food supply for the large 
and varied fauna of that time. At the close of that period a 
folding resulted in an uplift of a broad, flat island-like area about 
Cincinnati. This arch known as the Cincinnati axis traversed in 
a northeasterly direction from Tennessee and Kentucky to the 
lake basin into Canada. From that time on Ohio was nearer sea- 
level and in places the land areas were so far elevated as to allow 
sluggish streams and basins, bordered by plants (13, 4, 11). 
The Upper Silurian period includes the Saluba and Belfast 
beds, the highly crystalline Clinton limestone, the several elements 
of the Niagara group, and the Monroe formation. It extended 
over a vast period of time, pointing to oscillations of level which 
covered wide ranges of latitude. The great lagoons and inclosed 
salt-water basins which were present suffered rapid evaporation. 
They are signs indicating that an unusually arid atmosphere pre- 
vailed. The severity of the conditions restricted life almost 
wholly to the lowland and the shore of other more favorable 
regions. Probably the Arctic regions were then the most favor- 
able for growth and development. The fossil plants are few and 
at times of doubtful affinity; the data are altogether inadequate 
to give any idea of the vegetation and its ecological conditions for 
