April, 1911.] The Ancient Vegetation of Ohio. 313 



cause of the xerophily of many of the carboniferous plants which 

 lived in swampy areas. The present paper is intended therefore, 

 as a continuation of the ecological studies which appeared from 

 time to time on the vegetation of an Ohio bog and peat deposit. 

 (7-10). The problems involved in the following discussion are 

 by no means to be solved within the limits of this paper; merely 

 an adjustment of perspective is made, leading from a considera- 

 tion of the fossiliferous plant remains of the coal measures of Ohio. 



In attempting to sketch an outline of the geological history of 

 Ohio it is obviously impossible to go into any details of descrip- 

 tion, or closely follow the development up to the present. At 

 most only the briefest introduction can serve and only a general 

 resume can be noted here. For the specific Geology of the state 

 and a fuller treatment of the subject, the reader is referred to the 

 volumes of the Geological Survey of Ohio and to the literature 

 here cited. 



Were we to make a rock section deep enough to reach to the 

 lowest limits of the known stratified deposits, to the great founda- 

 tions of the continent, the geological strata underlying the state 

 would show as a stage of early growth a predominance of lime- 

 stone and shale in the lower half of the section, and as a stage of 

 relative maturity widespread horizons of sandstone and conglom- 

 erate in the upper half of the section. The strata would char- 

 acterize the gradual dominance of atmospheric over hydrospheric 

 and volcanic action in a succession of changes, often interrupted 

 and repeated, of which a mountainous elevation and the graded 

 plain near sea level are the extreme fonns in the physiographic 

 cycle. 



The strata belong to five principal divisions or ages which 

 named in ascending order are as follows: Lower vSilurian or 

 Ordovician; Upper vSilurian; Devonian; Sub-carboniferous or 

 Alississippian; and Carboniferous, Pennsylvanian, or Coal- 

 Aleasures. Over the northern and north-western half of the 

 state these are covered by heavy beds of clay, sand, and bowlders 

 which taken together constitute glacial drift. No evidences have 

 been found in Ohio of that group of strata below the Ordovician 

 known as the Cambrian, and pre-Cambrian (Laurentian, Huro- 

 nian and Keweenawan), or the great series of systems comprising 

 the Mesozoic and Tertiary time divisions. They either left no 

 record within the limits of the state, or much erosion must have 

 taken place immediately succeeding their formation. 



Each of the rock systems is again subdivided, and inasmuch as 

 the new stratigraphical divisions are coming into use more gener- 

 ally and are replacing the geological names of the older surveys, 

 the following table taken from Bulletin 7, (21), has been added to 

 show the place in the scale, the relationship of old and new names 

 for the fomiations, and the thickness assigned to the various 

 formations: 



