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 



