82 DONALD C. BARTON 
basement must be rising rapidly southward. Rosenheim and Holz- 
_ kirchen lie well north of the front overthrusts; the front of the Ba- 
varian Alps has been formed by overthrusting from the south; experi- 
ments seem to indicate that the front of the extensive yielding in over- 
_ thrusting lies along a 45° shear line; the weight of the overriding over- 
thrust sheets should tend to depress the basement, even for a con- 
siderable distance out into the foreland; the great thickness of the 
upturned Tertiary beds in the edge of the Alps would indicate corre- 
spondingly great thickness of the undisturbed Tertiary beds at Holz- 
kirchen and Rosenheim. A southward dip of the basement at those 
places, therefore, is geologically more probable than a southward rise. 
The observed southward decrease of Ag, is satisfactorily explained by 
the dip of the basement under the Tertiary beds. 
DIP OF BASEMENTS 
The divergent regional variation of Ag, and of Az, seems to indi- 
cate divergent slopes between the surface of the crystalline basement 
and some higher surface of discontinuity between generally heavier 
rocks below and generally lighter rocks above. 
The generally southerly decrease of gravity presumably is pro- 
duced by a southward dipping upper surface of a thick series of rocks 
heavier than the overlying rocks. Geologically, such a dip is probable. 
The Mesozoic beds immediately north of the Danube in general dip 
gently southward. The Tertiary section must thicken greatly south- 
ward to produce the very great thickness of Tertiary beds which are 
upturned at the front of the Alps. The basement on which the Ter- 
tiary beds rest must dip southward. The unconsolidated Tertiary 
beds are composed predominantly of sands, clays, and gravel and, 
therefore, are relatively light. The underlying, presumably mostly 
lower Mesozoic beds are much more consolidated, comprise much lime- 
stone and sandstone, and presumably must be relatively light. The 
surface on which the Tertiary beds rest, therefore, presumably is a 
surface of density discontinuity with heavier rocks below. Quantita- 
tively, with reasonable density assumptions, the observed gradient 
profile across the basin is produced by a geologically reasonable slope 
of that basement to the geologically reasonable thickness of uncon- 
solidated sediments at Rosenheim and Holzkircken of 13,000 feet 
(+25 per cent). 
The southerly decrease of Ag, across the basin mathematically also 
could be produced in whole or in part by a progressive horizontal 
variation in the character of the beds from unconsolidated sand and 
clay at the south to massive limestone at the north in a verticai sec- 
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