ECOLOGICAL SIGNIFICAXCE OF EAGLE CREEK FLORA 591 



climax forest of a mesophytic sort is estimated to be from one to 

 two hundred years. This is on the basis of there being no soil at 

 the outset, and of its development through the agencies of plants 

 and weathering. It also assumes a soil favorable for the reception 

 of plants. In the case of the soil furnished by the Eagle Creek 

 rocks, there was a distinct time advantage due to the fact that 

 they were not consolidated and therefore offered an immediate 

 foothold for rooted plants. On the other hand the chemical 

 composition of this sediment was probably quite unsuitable for 

 the growth of most higher plants, certainly for the growth of 

 mesophytes. The latter require a humus content which was 

 entirely lacking in the original volcanic materials. Further, due 

 to its basic composition, this may be supposed to have been quite 

 unfavorable for the development of such seedlings as germinated 

 in it. Experimental e\'idence has sho^-n that of seeds planted 

 in pulverized Eagle Creek rock from several locahties, only those 

 of oaks (xerophytes) developed successfully. The experiments 

 were not satisfactorily completed, and it is not known whether the 

 oak seedlings would have continued to develop in this soil. Obser- 

 vational evidence from regions recently covered by volcanic ash 

 indicate that a number of years may elapse before the return of 

 the higher plants. It is not unreasonable therefore to assume 

 that the full one to two hundred years would have been required 

 for the development of a climax mesophytic forest on the volcanic 

 debris-strew^n surface during Eagle Creek times. 



While it is not possible to correlate the various horizons which 

 contain plant remains in widely separated parts of the area, due 

 to their limited horizontal extent, it is possible to determine, on the 

 basis of relative elevation, that there are at least ten distinct 

 horizons represented. Each of these contains leaves of the climax 

 forest which, as we have seen, would require from one to two 

 centuries for its development. The total length of time involved 

 in the growth of the ten plant horizons may thus be placed at from 

 one to two thousand years. And when it is realized that there 

 must be numerous other plant-bearing horizons w^hich hav: not 

 been uncovered, the length of the epoch as inferred from plant 

 growth mav be greatlv extended. 



