1901 | PHYSIOGRAPHIC ECOLOGY OF CHICAGO 89 
as the cafion broadens out and the slopes become less steep, 
shrubs and trees come in, though a typical mesophytic forest is 
rarely seen.. The Starved rock ravines are cut in St. Peters 
sandstone, those at Lockport in the Niagara limestone, yet the 
vegetation in the two places is essentially alike; at any rate the 
resemblances are greater than the differences. Much has been 



IG. I.—Embryonic ravine in the lake bluff at Glencoe. Entire absence of 
eee on the unstable ae slopes with the exception of shrubs and grasses that 
have slid down from the t 
written on the physical and chemical influences of rocks upon 
the vegetation. The facts seen here seem to show that the 
phy siographic stage of a region is more important than either. 
The flora of a youthful topography in limestone, so far as the 
author has observed, more closely resembles the flora of a similar 
Stage in sandstone than a young limestone topography resembles 
an old limestone topography. A limestone ravine resembles a 
Sandstone ravine far more than a limestone ravine resembles an 
€xposed limestone bluff or a sandstone ravine resembles an 
