April, 1911.] The Ancient Vegetation of Ohio. 315 



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. 

 The}' 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 accmnulation 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 3'ield 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, fiat 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 fonnation. 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 suilered 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 



