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A ZONE OF LARGE CONCRETIONS IN THE KNOBSTONE. 
W. M. TUCKER. 
My attention was recently called to a peculiar and interesting bed 
of concretions in the Knobstone of Monroe County. The deposit is very 
local in its distribution. It occurs in two ravines in sections 1 and 2, 
T. 10 N., R. 3 W., in the northwest corner of Monroe County. The two 
ravines head on the Harrodsburg limestone near the middle of sections 
1 and 2 and extend northward, immediately entering the Knobstone 
with the characteristic rapids and small waterfalls. The main ravine 
(west) has a depth of seventy feet one-fourth of a mile from its 
source, and the smaller one (east) attains that depth in a shorter dis- 
tance. The larger ravine enters the concretionary zone thirty-five feet 
below the contact of the Harrodsburg and Knobstone. The zone is 
FIG. 1. 
Fig. 1. A coneretion five feet in diameter which has been dislodged from the ravine 
wall in the background. 
fifteen feet thick. The concretions can be seen in the ravine walls for 
about one-fourth of a mile, just south of the Monroe County line (Figs. 
1 and 2). The bottom of the ravine is strewn with concretions and 
fragments for this distance. Only four were found in the smaller 
ravine which at this point is about one-quarter of a mile east. None 
were found in the other ravines of the neighborhood. 
The concretions vary in size from a fraction of an inch to five 
feet in diameter. They show none of the concentric structure which 
is displayed in some concretions. No distinct nucleus was discovered in 
any of them. The composition of the concretions is highly silicious, 
especially those in the upper part of the zone. Those in the lower 
