584 RALPH W. CHANEY 
There is little reason to doubt that these two ecological types 
represent two distinct habitats from which leaves have become 
intermingled and fossilized. The abundance of individual oak 
leaves is adequate evidence that they have not come from scattered 
relicts of an earlier succession which has been supplanted by one 
more mesophytic. On the assumption that the xerophytic leaves 
are xeromorphs and owe their structure to a physiologically dry 
habitat such as a bog, a twofold habitat would still be required, 
for such xeromorphic forms would not be included in the same 
association with typical mesophytes like Acer, Ulmus, and Platanus. 
Further, the typical xeromorphic leaf is entire-margined, while 
Quercus pseudo-lyrata has conspicuous lobes and sinuses. On the 
basis then of two habitats contributing leaves, we may consider 
the general type of topography required by the plant evidence. 
In many parts of the United States today the uplands are 
occupied by a xerophytic oak association due to the exposure of 
such a habitat to the sun and the wind, and the consequent high 
rate of evaporation. Where such an upland is dissected by valleys, 
especially by those with rather deep and narrow dimensions, these 
more protected situations may furnish conditions favorable for 
the development of a typical mesophytic flora. We may have, then, 
as a common occurrence, a xerophytic upland association with 
mesophytic tracts along the streams. Leaves from the upland 
trees are transported widely, due to exposure to winds, and may 
be carried down into the valleys and mixed with those of the 
mesophytes growing there. Such situations are so common today 
that there is little danger in assuming that they were common 
during the Eagle Creek epoch, though the geological evidence of 
such topography should be forthcoming if such were the case. On 
the basis of the plants, however, it is reasonable to assume the 
existence of this upland habitat, supporting an oak forest, and 
occasional valleys occupied by mesophytic maples, elms, and other 
species. 
The mixture of the xerophytic and mesophytic types of leaves 
may thus be explained on the basis that the former were brought 
in from above and mixed with the mesophytes in the valley deposits. 
Aside from the exposed situation of the uplands, which would 
