363 
here given of geologic structure as a physiographic term is intended to be 
applied to a plains region. Under the term geologic structure are included 
the types of regional rock and the lithologic succession, as well as the in- 
clination of the strata. Essentially this is the descriptive stratigraphy and 
the regional dip of the rock. It is lithology and structure. A physiographic 
paper need have no more of this phase of geology given than is necessary 
to show the responsibility of the inclination of the strata, the type of rock, 
and the relationship of the rock layers as conditioning factors in the deyel- 
= ae 
. 
L 
‘ 
te 
S 
N 
Be 10 20 30 40 50 
SCALE OF MILES 
OUTLINE MAP OF SOUTHERN INDIANA 
SHOWING LOCATION OF AREA 
TREATED AS AN EXAMPLE OF 
EXPLANATORY PHYSIOC RAPHY 
opment of topographic forms. It is the intention of the writer in this 
paper, however, to show specifically that the topographic forms present in 
the stages of youth and maturity are dependent very largely upon lithology 
and structure. 
Topographic condition is the state of a region with respect to the form, 
size, and relationship of the relief features. The simplest topographic con- 
dition is that of a level plain. The coastal plain is an example. The topo- 
graphic condition becomes more complex as relief or difference in elevation 
from place to place is produced by the physiographic processes, chief of 
which is running water. Essentially. topographic condition is expressed 
generally by stating the stage of topographic development in terms of the 
