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SCIENCE 



[N. S. Vol. XXVI. No. 655 



ness, then revived erosion may produce, in the 

 early youth of the new cycle, a fault-line 

 valley; the work of a consequent or of a sub- 

 sequent stream, as the case may be. 



This problem is only a special phase of the 

 general treatment of faults from the physio- 

 graphic instead of from the geologic point of 

 view. For the geologist, once a fault, always 

 a fault; displacement, length, heaved block, 

 thrown block, etc., retain their values and 

 their names indefinitely. For the physiog- 

 rapher, once a fault scarp, afterwards some- 

 thing else: the scarp retreats from the fault 

 line; inequality of level across the fault line 

 ordinarily decreases and ultimately vanishes, 

 but it may for a time be reversed even in the 

 first cycle of erosion; if a completed cycle is 

 followed by uplift, revived erosion may pro- 

 duce a narrow fault-line valley; or a fault- 

 line scarp, the aspect, height and length of 

 which have no definite relation to the aspect 

 and dimensions of the original displacement. 

 The effects of insufficient attention to the 

 physiographic aspects of faulting are illus- 

 trated in the following note, as well as in a 

 current discussion on " How should faults be 

 named and classified " in the Economic Geolo- 

 gist, where consideration is given only the 

 underground elements, as is natural enough in 

 a geological discussion, though somewhat in- 

 appropriate to the general title under which 

 the discussion has been carried on. 



FAULT-LINE SCAEPS IN SWEDEN 



The uplands of central Sweden possess a 

 number of well-defined scarps, which are de- 

 scribed by Gunnar Andersson as due to fault- 

 ing, with only subordinate modification by 

 erosion, (" Om Malaretrakternas geografi," 

 Ymer - iidshnft utgifven of Svensha sallskabet 

 for antropologi och geografi, 1903, 1-64). For 

 reasons stated below, these features are better 

 interpreted as fault-line scarps; but however 

 they are regarded, they give no countenance 

 whatever for drawing rectilinear structural 

 lines or " lineaments " between points from 

 which earthquake reports are received. It 

 is true that many of the Swedish scarps 

 have a rough east-west trend; but it would be 



quite impossible to determine the further ex- 

 tension of any one of them by continuing the 

 trend of even the least curved part of its ir- 

 regular course. These fault lines, along with 

 many others, prove that the highly exceptional 

 quality of a straight line is not to be expected 

 in crustal dislocations. 



Andersson infers a modern (Tertiary) date 

 for the faults of central Sweden, because the 

 scarps along the fault lines are still well de- 

 fined; but in reaching this conclusion he has 

 taken no account of the possibility of two 

 cycles of erosion. He argues that, if the 

 faults were ancient, their scarps would have 

 been long ago planed down by erosion. On 

 the other hand, it is manifest that even if the 

 faults were of paleozoic date, the scarps might 

 be distinct to-day if, after having been base- 

 leveled, they were re-developed by the removal 

 of weak rocks along one side of the fault line 

 in a new cycle of erosion. That at least two 

 cycles of erosion since the period of faulting 

 must here be reckoned with is strongly indi- 

 cated by the occurrence of numerous narrow 

 fault -line valleys through districts of resistant 

 crystalline rocks; the uplands on either side 

 being of essentially equal height. An account 

 of some striking examples of these narrow 

 valleys is given by A. Larsson, " Topografiska 

 studier i Stockholmstrakten," Ymer, 1906, 

 273-292. Near by, along parts of the same 

 fault lines or of similar fault lines, well-de- 

 fined scarps separate uplands of crystalline 

 rocks from lowlands in which the crystallines 

 are at least in some instances patched with 

 small remnants of a former unconformable 

 cover of relatively weak paleozoic strata. In 

 these instances there is good reason for think- 

 ing that the now lower ground was, at the 

 beginning of the present cycle of erosion, filled 

 up to the level of the crystalline uplands with 

 the paleozoic strata; and hence that while the 

 erosion by which the fault-line scarps were 

 developed may well be of Tertiary date, the 

 date of the faults must be decidedly earlier. 



The district here considered, lying not far 

 west of Stockholm, will presumably be visited 

 by excursions at the time of the next Interna- 

 tional Geological Congress in 1910. It is as 



