185 R. W. CLARK AND HOLBROOK G. BOTSET 
quite well known. The authors acknowledge their indebtedness to 
A. E. Ruark, of the University of Pittsburgh, and Paul Weaver, 
Houston, Texas, for valuable suggestions in the conduct of this work. 
APPARATUS AND FIELD METHODS 
The measurements were made in soils which were developed over 
sedimentary formations consisting predominantly of sandy clays with 


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Fic. 1.—Diagrammatic section of radon measuring apparatus. 
some slightly consolidated sands, all of Tertiary age. Most of the 
measurements were made in wooded areas, but some were in culti- 
vated fields, and some in natural prairies. 
The technique of making the measurements is a modification of 
the method developed by Ambronn.! The equipment used is shown 
diagrammatically in Figure 1. The hole into which the sampling tube 
is placed is made by first driving a steel rod into the ground about a 
foot and then continuing the hole with an earth auger. This is to 
1R Ambronn, Elements of Geophysics, English translation by Cobb (1928), p. 119. 
510 
