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 forms in the physiographic 
cycle. 
The strata belong to five principal divisions or ages which 
named in ascending order are as follows: Lower Silurian or 
Ordovician; Upper Silurian; Devonian; Sub-carboniferous or 
Mississippian ; and Carboniferous, Pennsylvanian, or Coal- 
Measures. 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 formations, and the thickness assigned to the various 
formations: 
