384 E. LUCY BRAUN 



and (4) occasionally near the tops of the higher hills. Slabs 

 of limestone weathered out from the bed-rock are numerous on 

 the steeper hillsides. In the first two types of locations, the 

 rocks are subjected usually several times annually, to the erosive 

 action of streams. In the third type, conditions of light and 

 moisture are extreme, especially in those quarries recently 

 worked. When the quarry has been long abandoned, the face 

 is almost covered with soil and small rock fragments, thus giv- 

 ing adequate foothold for herbaceous and even tree growth. 

 The fourth type of location, rock outcrops near the tops of 

 the higher hills, is somewhat similar to the conglomerate out- 

 crops under consideration. Even here, the rock succession^ is 

 very incomplete, only the earliest lichen and moss stages being 

 represented before the advent of herbaceous and woody plants, 

 which appear relatively early because of the many crevices. 

 Because of the position, high up on slopes, the rocks are always 

 exposed to direct sunlight, until shaded by their own vegetation. 

 The limestone slabs lying on the surface of steeper hillsides are 

 so small that they can only support a very meager flora. 



The character and frequency of rock outcrops in the Cincin- 

 nati region has been given here in order to make clear the de- 

 gree of isolation of the conglomerate rock areas in the region. 

 The vegetation of these rocks is of interest chiefly because of 

 its unusualness in the region. It is of a character to be expected 

 in a rocky region, where migration from area to area is easy. 

 It is remarkable in a region of few stable rock outcrops, where 

 distance becomes an obstacle to migration. 



VEGETATION 



The plant succession of the conglomerate rocks of the Cincin- 

 nati region is the only typical rock succession in the region. 

 The succession passes through various lichen and moss stages 

 before the advent of herbaceous and shrub stages. 



1. Lichen stages. The lichen stages of the succession are two 



1 Braun, E. Lucy. The Physiographic Ecology of the Cincinnati Region. 

 Ohio Biol. Survey, Bulletin 7, 1916. 



i 



