86 DONALD C. BARTON 
west front of the Bohemian massif. Over that stretch, the Danube 
flows at the foot of the edge of the crystalline rocks of the Bohemian 
massif. But from Hofkirchen past Passau, the Danube flows across 
the crystalline rocks, and a cross (northeast-southwest) fault is shown 
by Schuster’s map at Hofkirchen. The structural block southeast of 
Hofkirchen geologically seems to have been uplifted; or the structural 
block northwest of Hofkirchen and in front of the crystallines geo- 
logically would seem to have been dropped down. 
The broad flat-topped magnetic maximum in the area south of 
Hofkirchen, and west and southwest of Passau, and the magnetic 
minimum which extends from the vicinity of Hofkirchen northwest- 
ward along the Danube are in agreement with the picture of the rela- 
tively uplifted block south and west of Passau and Hofkirchen and the 
relatively down-dropped block northeast of Hofkirchen (Fig. 7). 
The throw of the Danubian fault from Regensburg to Hofkirchen, 
on the basis of the magnetic data would seem not to be large. That 
fault brings the sediments in fault contact with the crystalline rocks. 
If the throw of the fault were large, there would be a sharp jump in the 
magnetic intensity at the contact. A sharp jump was observed on a 
traverse across the contact a short distance northwest of Deggendorf; 
but on the other traverses across the contact, its presence was dubi- 
ously reflected in the observed magnetic picture. There are two con- 
trasting @ priori alternatives in regard to that Danubian fault: (1) the 
sediments may have transgressed up the southwesterly dipping sur- 
face of the crystalline rocks, and a fault of moderate throw (100-200 
meters) may have dropped the basinward sediments down only that 
moderate distance; or (2) progressive movement along the fault may 
have carried the basement of the basinward block down concomi- 
tantly with the general subsidence of the basin and with the deposi- 
tion of a thick prism of sediments in the basin. Under the second hy- 
pothesis, there would be great thickening of the Tertiary sediments 
only a short distance out from the fault. The slight magnetic anomaly 
at the contact indicates that the throw of the Regensburg-Hofkirchen 
fault is 100 or 200 meters rather than 1,000 or 2,000 meters. 
Three westward facing structural scarps, or extra steep slopes, 
presumably fault scarps, on the subsurface flank of the Bohemian 
crystalline massif are suggested by closer spacing of the isogams along 
certain zones. Faint regional features are obscured by the numerous 
lesser featuses. But if the isogams are smoothed out as well as possible 
to show their normal or regional course without regard to the lesser, 
local irregularities, there seems to be less than normal spacing between 
the 575- and 625-gamma isogams, in the zone from Strauburg south- 
608 
