MAGNETIC VECTOR STUDIES 105 
the locations of the first wells and the isogams based on 12 magnet- 
ometer stations. The isogams check fairly well with the contour lines 
drawn on the red beds of the Coldwater, but in contradiction to 
current geological conceptions, seem to be in favor of the local mag- 
netic vector, suggesting a northeast-southwesterly trend of the 
structure. Though the production from the Traverse has been dis- 
appointing so far, there seems to be no doubt that the magnetic data 
indicate a considerable uplift. 
It is, however, rather surprising that the magnetic “high” should 
so closely correspond with the structural “‘high”’ in the Traverse. The 
rule for Michigan will most probably be that the magnetic “high,” 
which is caused by an anticlinal structure in the Basement complex, 
is considerably offset from the structural “high” in the Dundee or 
Traverse, mainly because of the several hundred feet of plastic salt 
and anhydrite beds, which lie between the upper and lower structure. 
Since the gravimetric field may reasonably be assumed to show 
some influence of upper structures, it seems that a combination of 
gravimetric and magnetic data may lead to the discovery of commer- 
cial structures in such areas, which, like large parts of Canada, are 
covered by several hundred feet of unconsolidated glacial drift. 
The application of three-dimensional magnetic prospecting is lia- 
ble to improve a great deal the chance of locating commercial struc- 
tures magnetically. By publishing these vector maps, it is notso much 
the writer’s intention, however, to draw renewed attention to the 
magnetic method at the expense of other geophysical methods, but 
rather to encourage magnetic investigations as a great help for the 
interpretation of results gained especially by the gravimetric and seis- 
mic methods. Both these methods work, as a rule, on beds considera- 
bly above the magnetically active horizons, and in many cases, only 
the combination of their data with the data gained magnetically from 
deeper strata will lead to a proper geological interpretation of the 
gravimetric and seismic indications obtained in a certain area. 
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