Erosion Cycles in Xnrfli iresfern Illinois. — I/cfsJiet/. (3 
The strata are nearly horizontal, the normal dip being to 
the south at the rate of a few feet per mile. But they have 
been thrown into gentle undulations of two systems. The iirst 
S3\stem consists of a number of low broad anticlinal and mo- 
noclinal axes sweeping across the district in a general east 
and west direction, but curving slightly toward the south. 
Crossing this sj^stem at an oblique angle, there is a less dis- 
tinct northwest and southeast system. In addition to the 
above systems of a true Appalachian montanic type, there is 
a long broad structural elevation, commonly known as the 
Grand de Tour-La Salle anticlinal. This is the nature of the 
so-called Cincinnati arch, of which, in fact, it appears to be a 
continuation. 
Topography. 
In order to obtain a correct idea of the topographic features 
of the district under discussion, we can do no better than to 
briefly describe a number of views taken from elevated sta- 
tions within its limits. 
View 1. Two miles northwest of the town of Lena, in Ste- 
phenson county, there stands an isolated "mound," long 
thought to be the highest elevation in the state. In ascending 
it, a splendid scene bursts upon our vision. Few people know 
the delight of looking down upon a cultivated plain from even 
so low an elevation as a "mound." This hill is about 150 feet 
in hight, and it stands on a plain which has at tirst a gently 
rolling surface, but at some distance, if we face the north or 
east, toward the Pecatonica river, it becomes rapidly undu- 
lating, being dissected by comparatively narrow valleys. Al- 
though it is a hilly country, all the hilltops rise to nearl}^ the 
sanu' hight and in the far distance merge into a perfectly 
even sky line. Looking southeastward, the apparent plain is 
seen to be broken l\y a single elevation, a "mound," six miles 
distant, consisting of several long and narrow parallel ridges, 
wliich rise to a maximum altitude of about 125 feet above the 
plain. Southward and westward the level plain is terminated 
by a long range of hills, which, if the atmosphere be hazy, will 
resemble a low mountain range, though only a few hundred 
feet high and twelve miles distant. At the northern end, 
this range of hills breaks up into several isolated cone-shaped 
mounds. 
