Geological and topographical maps, their interpretation and use, a handbook for the geologist and civil engineer . neach case printed on the downthrow side, the throw ofthe main fault ab is only 30 feet at a, but the cross-fault, (X b 30 Ft. oC 200 Ft.\ 250 Ft. /X f \d 4 150 Ft 100 Ftf Fig. 49. c, with its downthrow of 170 feet, increases this to 200feet, which is still further modified by the throws of d, e,and/. A series of parallel faults may all throw in the samedirection, thus producing step-faults, as in Fig. 50, or theymay fall in opposite directions, giving an arrangementsimilar to tha
Geological and topographical maps, their interpretation and use, a handbook for the geologist and civil engineer . neach case printed on the downthrow side, the throw ofthe main fault ab is only 30 feet at a, but the cross-fault, (X b 30 Ft. oC 200 Ft.\ 250 Ft. /X f \d 4 150 Ft 100 Ftf Fig. 49. c, with its downthrow of 170 feet, increases this to 200feet, which is still further modified by the throws of d, e,and/. A series of parallel faults may all throw in the samedirection, thus producing step-faults, as in Fig. 50, or theymay fall in opposite directions, giving an arrangementsimilar to that of a syncline, and known as a trough-fault(Fig. 51). Ridge-faults as in Fig. 52 also occur. 74 GEOLOGICAL AND TOPOGRAPHICAL MAPS When a fault traverses more than one geological for-mation, the throw of the lower group of rocks may beconsiderably greater than that of the upper series. Thisis due to repetition of faulting along the same line offracture. Thus in Fig. 53, which is a section of such afault, the first movement took place after the formation ofthe Coal Measures, and amounted to some 970 feet. This.
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