SUWA BASIN, NEAR KYOTO, JAPAN 59 
rection formula derived by C. A. Heiland*? seems to be the most 
reasonable at present, and was used for the correction. 
The results of density determination on a large number of sam- 
ples of rocks and soils are shown in Table I. 
TABLE I 
DENSITY OF Rocks AND SoILs 
Names of Rocks Specific Samples are Taken from 
Gravity 
Contact metamorphosed (rock) 3-05 
Andesite Fe Ss 
Granite 272 
Diabase 2.70 
Conglomerate 2.66 
Diabasic tuff 2.65 
Gabbro? 2.64 
Tuff 2.44 
Andesite 2.43 Kosaka Pass 
Mean 2.71 
Soil age Road 
Soil 1.52 House lot or garden 
Soil 1.48 Field 
Mean 1.53 
The densities of rocks surrounding the Suwa Basin differ, but 
from the nature of rock distribution, it was confirmed that by taking 
the mean density of 2.71, an error of more than 5 per cent would 
not arise. Hence, the density of soil was taken as 1.53 and that of 
rock was taken as 2.71 in the computation. 
The topographic corrections were made in three stages as shown 
in Table II. 
TABLE II 
AREA OF TOPOGRAPHIC CORRECTION 
Stage Radius in Meters with Observation Maps Used for Drawing 
Station as Center; Corrected Area Profiles 
I 40 Surveyed by plane table 
2 5,000 Topographic map 
Scale: 1/50,000 
B 20 , O00 Topographic map 
Scale: 1/200,000 
The corrected value from the three stages (Table II) was maximum 
in the second stage and was minimum in the first stage, due to the 
attention given in selecting the stations. The normal correction is 
the correction for the longitude of the station and has nothing to do 
with the latitude. The difference in longitudes between the extreme 
-northern and southern observation stations was only 5.6 minutes. 
3C. A. Heiland, ‘““A New Graphical Method for Torsion Balance-Topographic 
Corrections and Interpretations,”’ Bull. Amer. Assoc. Petrol. Geol., Vol. 13, No. 1 (Janu- 
ary, 1929), Pp. 39-74. 
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