94 DONALD C. BARTON 
ALB BASALTIC AXIS 
The Alb magnetic maximum (Fig. 10) on the northwest edge of 
the area surveyed indicates the presence of an elongate intrusion or a 
line of intrusions parallel with the Danube line. The data mostly have 
been taken from Haussmann.‘ The results of the B.M.I. line from Ulm 
northwestward corroborate its presence although they place the 
southeast slope of the ridge of maximum north of Ulm rather than east 
of Ulm, as Haussmann delineates it. The writer agrees with Hauss- 
mann that the Alb axis of magnetic maximum must reflect the 
presence of a large basic igneous intrusion at depths of 3—8 kilometers. 
But Haussmann’s magnetic stations are too widely scattered to show 
whether there is one large intrusion or whether there are a series of 
intrusions whose magnetic effects merge and give the effect of one 
large intrusion. 
DONAU MOOS AXIS 
The Donau Moos axis of magnetic minimum (Fig. 10) south of the 
Danube axis of maximum is not so sharp or definitely delineated. Yet 
it does seem to exist and to parallel that Danube axis. There is a 
suggestion that the line is made up of a series of local minima, which 
are paired with, and southeast of, the maxima of the Danube line. 
A volcanic plug which has a large vertical dimension may act as a bar 
magnet; if it is vertical or nearly vertical and has only induced mag- 
netism, its upper pole will produce a maximum and its lower pole a 
much weaker minimum. If a volcanic plug dipped 75°—80° toward the 
southeast in Bavaria, and if it were polarized, the lower pole would 
tend to produce a weak minimum to the southeast of the maximum. 
This minimum does not indicate the presence of any structure sepa- 
rate from the volcanic plug and must not be confused with the or- 
dinary minima which represent lows in the ordinary (positive) inten- 
sity. South of Ingolstadt, there is a gravity minimum which is fully 
as definite as the magnetic minimum. The two minima are offset from 
each other 5 or 6 kilometers, but they appear to belong together and 
are reflecting a common structural feature. But if the two are pro- 
duced by a common structural feature, the minimum can not be pro- 
duced by the lower pole of an Ingolstadt volcanic plug, but must be 
produced by some structural feature which is independent from, but 
perhaps associated with, the Ingolstadt structure. The gravity mini- 
mum, presumably, must indicate a syncline. It therefore would tend 
to indicate that the Donau Moos axis indicates a syncline (or graben). 
° Karl Haussmann, “Magnetische Messungen um Ries und Dessen Umgeburg,” 
Abh. d. k. Preuss (Akademie der Wissenschaff, 1904). 
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