PAPERS ON BIOLOGY AND AGRICULTURE 171 



County. Cornus paniculata occurs in such a variety of 

 situations as to be almost a ubiquitous woodland species. 



One of the most interesting displays of oaks is to be 

 found just west of Grand Detour on the eroded anticline 

 of the structural defomiation crossing the Rock at that 

 place and forming the rock bluffs on the north shore of 

 the river in its western course beyond Grand Detour. The 

 assemblages include Quercus velutina, Q. ellipsoidalis in 

 its type form and its three varieties of intermedia, de- 

 pressa, and coronaria, Q. alba, Q. rubra, and Q. macrocai-pa, 

 the last species being nearby at least. These woods exhibit, 

 in their part on the tops of the sandstone bluffs, but not in 

 the portion farther back from the river, the substitution 

 of an oak stage in the succession for a coniferous stage. 

 The recession of conifers in this county is to be explained 

 not alone by the fact of their becoming relics of a past 

 climatic circle but also by the fact of man's operations of 

 cutting and clearing. Probably if Pinus strobus had 

 chanced to be present in the neighborhood of these sand- 

 stone bluffs in sufficient numbers to effect migration and 

 establishment, a white pine stage would have occurred in 

 the succession before the oaks, as is customary in this 

 section of the country, where the series pines-black oaks- 

 white oak-red oak, (hickory) — up to the climax, skeleton- 

 izes the succession in part. Here, however, the white pine 

 was not present in sufficient numbers to establish itself in new 

 territory'. That it is still able to do so, when present in 

 sufficient numbers to form a nucleus for migration, is de- 

 monstrated in the notable instance of the white pine woods 

 on the limestone bluff of Pine Creek in Pine Creek town- 

 ship. 



At the sandstone bluffs west of Grand Detour a dry. 

 sandy bank rises from shortly beyond the river side and 

 continues as a sandy site on top of the bluffs. Wherever 

 the vegetation has been able to advance considerably the 

 sandiness has become modified by the accumulation of 

 humus. The streamside species. Salix fluviatilis, S. nigra, 

 and Acer negundo. are frequent along the river. The lower 

 bank contains such species also. The moisture conditions 

 below the surface are there hydro-mesophytic. Fraxinus 



