SURVEY OF MUNICH TERTIARY BASIN 71 
The torsion-balance survey (Fig. 1) comprised 1,195 reconnais- 
sance stations and 366 detail stations. The reconnaissance stations 
are disposed: (1) in two north-south lines, one from the Danube at 
Ingolstadt to the edge of the foothills at Holzkirchen, and the other 
from Landshut to the foothills at Rosenheim; and (2) in a composite 
east-west line through the central part of the basin. A station interval 
of 200 meters was used on the Ingolstadt-Holzkirchen traverse in 
order to detect structures with narrow anomalies as well as structures 
with large anomalies and to determine the degree of surface irregu- 
larity of density. The station interval subsequently was increased 
to 400 and 600 meters. A latitude correction of 8E was used in the 
routine calculation of the gradient. The gradient effect of the Alps 
was neglected; the gradient which is produced at Sauerlach by the 
topographic mass of the Alps was calculated to be +1.4 for U..; as 
that gradient varies slowly and smoothly and is small compared with 
the observed gradient, it need not be eliminated unless quantitative 
calculations of structural profiles are made or unless the position of 
structures near the foot of the mountains needs to be determined with 
high accuracy. 
The magnetic survey (Fig. 1) comprised 14,743 stations with a 
Schmidt-Lloyd vertical variometer. Those stations are disposed in a 
criss-cross series of reconnaissance traverses which covered thoroughly 
the whole of the Munich Tertiary basin and which extended into the 
foothills of the Alps on the south, and across the Danube into the 
Frankish-Schwabian Jura on the north, and the area of the Bohemian 
massif on the northeast. A primary base line of magnetic benchmarks 
was run between Ingolstadt and Holzkirchen; the value of Az was 
determined by rapid runs in an automobile between benchmarks until 
a consistent series of determinations was obtained; from that base 
line, a net of primary benchmarks was similarly established through 
the rest of the area. The traverse lines were adjusted to those primary 
benchmarks and to each other. A station interval of 200-300 meters 
was used on most of the traverses. Careful checking back and careful 
checking in on base stations and benchmarks was practiced. Correc- 
tions were applied for the fluctuations of the intensity of the earth’s 
magnetic field as observed at Pottsdam. The foliowing correction for 
the normal increase of intensity with magnetic latitude was applied 
in a routine manner in the station calculations: +8y per 1 minute of 
increase of (astronomic) latitude and —1.57 per 1 minute of increase 
of longitude. The magnetic survey was run as an inexpensive and 
rapid method of possibly supplementing the slower and more costly 
_ torsion-balance survey. The expectations of it were not great. 
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