100 Trans. Acad. Sei. of St. Louis. 
times rising to a height of two or three hundred feet 
above the flood plains. 
Where the course of the stream has led through the 
usual limestone formations of the region portions of the 
valley are from half a mile to a mile in width. However 
when the level of the Grand Falls Chert was reached the 
process of erosion was sharply checked, and a series of 
shallows and rapids were formed, as the water, etching 
its way slowly through the hard strata, leaped from ledge 
to ledge. This change in the topography of the valley 
is well shown on the map, where the contour lines are 
crowded close to the stream in the vicinity of Reding’s 
Mill. Three miles below the rapids culminate in the 
Grand Falls, where the stream makes a drop of twenty- 
four feet. For most of the intervening distance the 
ereek has cut through the upper layers of the chert, which 
is exposed on one or both sides in perpendicular or over- 
hanging cliffs, twenty to forty feet in height. Extending 
for some distance back from the tops of these cliffs the 
rock has been washed bare or is covered only with a 
sparse mantle of soil, thus forming the barrens. 
So hard and dense is the rock that the ordinary forces 
of surface erosion: rain, wind and frost, have little effect 
upon it. Looking at the gnarled and rugged faces of the 
cliffs or at the smoothly polished promontories of the sur- 
face, one might well believe that the storms of ages would 
beat upon them to little purpose. Indeed few works of 
nature impress the mind more forcibly with a sense of 
their strength and indestructibility than these massive 
beds of the Grand Falls Chert. 
The stream, however, aided by the sharp gravel and 
boulders derived from the beds themselves, is slowly but 
incessantly cutting its way through them, and in places 
undermining the cliffs. The process of disintegration is 
facilitated by the fact that the rock is deeply fractured at 
intervals by fissures, either vertical or at various angles, 
that eventually allow undermined portions of the cliffs to 
shear off into the stream. Here and there great castle- 
