100 BOTANICAL GAZETTE [FEBRUARY 
almost at right angles to the shore line. It will thus be seen 
that the most favorable theoretical locality for dunes in a region 
of northwest winds is on the southeast shore of a body of water 
in that region. As a matter of fact, the dune region increases 
in area and the dunes themselves increase in height and com- 
plexity as one passes from Chicago around the south end of 
Lake Michigan. The culmination of the dune formations actually 
occurs between Dune Park and Michigan City, and an examina 
tion of the accompanying map (fig. 7) will show that these 
localities have a shore line running nearly southwest to north: 
east. The contour of the dunes themselves also shows that they 
were shaped by northwest winds, as does the path formed by the 
sweeping of the wind. 
The Dune Park region furnishes the most extensive area of 
present dune activity to be found along the southern coast of 
Lake Michigan, although the altitudes of individual dunes att 
much greater at many points in Michigan. Elsewhere the activé 
dunes are usually confined to a very narrow belt fringing the 
shore, but at Dune Park the dunes are active from one to tw 
kilometers inland, the front of the advancing dunes varyilg 
from 6 to 30 meters in height. The dune complex or area of 
dune activity at Dune Park covers perhaps 1000 hectare 
The established dunes here as elsewhere cover a far grealet } 
area than do the active dunes, reaching inland three to eight | 
kilometers. Between Chicago and Dune Park there is 4 mot : 
interesting series of parallel ridges, alternating with depressiom® 1 
which often reach below the water level throughout the call? | 
year. The origin of these ridges is scarcely within the provine: 4 
of this paper; their extreme regularity of contour, in addition” 
their persistent parallelism, seems hardly consonant with a pe : 
Sot d hee 
origin. Because of the low altitude of these ridges ane 
protection from shore conditions, their flora is not tyP! . 
xerophytic. Whatever the origin of these ridges, they f é m4 
a phase in the lake’s history when its waters were much iat | 
inland than at present. The active dunes at Dune Park 2 
scarcely ever more than 30 meters in altitude, but there | 
