THE FERN BULLETIN 



Vol. XX JANUARY, 1912 No. 1 



THE ROCK RELATIONS OF THE CLIFF-BRAKES. 



BY E. J. HILL. 



The note under Pteridographia in the Fern Bulletin 

 for July, 19 11, concerning Pellaea gracilis on sandstone 

 and its unusual occurrence on any rocks except lime- 

 stone, reminds me of a similar experience with it, and 

 of another station to be added to the two that are men- 

 tioned. In July 1905, on an excursion with the Chicago 

 Academy of Sciences, I collected this fern on a moist, 

 shaded sandstone cliff outcropping on the sides of Lib- 

 erty Hill, which overlooks the village of Oregon, Illi- 

 nois. The prevailing rock here is the St. Peters sand- 

 stone. The Trenton Limestone lies next above, but did 

 not outcrop at the point where the fern grew. The 

 sandstone is ferruginous, usually soft and friable, but 

 sometimes so hardened by the iron which forms the 

 chief cementing material as to ring like a piece of old 

 casting when struck by a hammer. Such was the 

 character of the sandstone that formed the mass of 

 Liberty Hill. The three other localities in Illinois — - 

 the only state in which I have yet found it — Kankakee^ 

 and in Cook County, . Lemont and Sag Bridge, were 

 on outcrops of Niagara Limestone. 



As the relation of this slender cliff brake as well 

 as of the larger Pellaea atropurpurea to the underlying 

 rock is a matter of interest, it may be well to report my 

 experience with this also, and draw some conclusions 

 from their character. In another locality near Oregon 

 on the same excursion, I collected this fern on the 



