112 AMERICAN FERN JOURNAL 
there are two main formations, one a very hard white 
sandstone, and the other a soft shale. I am informed 
by surveyors of the U. S. Geological Survey that only 
one outcrop of limestone occurs in the immediate 
vicinity of Rock Enon, and that is in a dry, open field, 
and contains no ferns whatever. 
At Natural Bridge, Filix bulbifera, Pellaea atropur- 
purea, Asplenium angustifolium, A. Ruta-muraria, Camp- 
tosorus rhizophyllus were found in the greatest abund- 
ance, while the shield ferns were represented by only 
one species, Dryopteris marginalis. Asplenium mon- 
tanum was represented by a single colony which was 
located on the sandstone ridge. At Rock Enon, Filix 
bulbifera, Camptosorus rhizophyllus, Asplenium Ruta- 
muraria, and Asplenium angustifolium were absent 
entirely, and only a few plants of Pellaca atropurpurea 
were found. On the other hand, Asplenium montanum 
occurred in abundance, the shield ferns were well repre- 
sented, and a fair sized colony of Asplenium Bradleyt 
was found. Cheilanthes lanosa grew only on the shale 
formation. It is apparent, therefore, that A. angusti- 
folium, A. Ruta-muraria, F. bulbifera, C. rhizophyllus, 
and P. atropurpurea prefer a basic soil, such as is found 
at Natural Bridge, whereas A. montanum and C. 
lanosa prefer the acid soil of Rock Enon. This is further 
borne out, at least as far as P. atropurpurea is concerned, 
by the fact that we have noted perhaps half a dozen 
localities around Washington and Baltimore, where 
P. atropurpurea was found growing in the mortar on 
old walls. Members of the Society will remember the 
profusion of A. angustifolium, F. bulbifera, and C. rhizo- 
phyllus growing on the limestone formation at James- 
ville, New York. These preferences of various ferns 
for certain kinds of soil are, of course, not at all new, 
but the present instance serves to emphasize the point 
in question. 
