292 G. K. Gilbert — Inculcation of Scientific Method. 



great inductions of geology that as the ages roll by the surface 

 of the earth rises and falls in a way that may be called undula- 

 tory. I do not now refer to the anticlinal and synclinal flex- 

 ures of strata, so conspicuous in some mountainous regions,but 

 to broader and far gentler flexures which are inconstant in 

 position from period to period. By such undulations the Ter- 

 tiary lake basins of the Far West were not only formed but 

 were remodeled and rearranged many times. By such undula- 

 tions the basin of Great Salt Lake was created. As to their 

 cause, geology is absolutely ignorant, and she is almost abso- 

 lutely silent. When it was ascertained that the Bonneville 

 shore-line attwodistant points had not the same height, the first 

 hypothesis to suggest itself merely referred the difference to 

 this gentle undulatory movement of the crust. As other hy- 

 potheses are to be mentioned, it will be convenient to christen 

 this one the hypothesis of unexplained undulation. 



A few years later the discovery was made that a fault had 

 occurred along the western base of the Wasatch range of moun- 

 tains since the Bonneville epoch. This range lies just east of 

 Great Salt Lake, and the Bonneville shore is traced across its 

 western face. The effect of the fault was to lift the mountain 

 higher, with reference to the lake bottom, and to carry that 

 part of the old shore-line upward. The amount of the uplift 

 varied in different parts of the fault from ten to fifty feet. 



This discovery was something more than the finding of a 

 post-Bonneville fault; it was the discovery also of a new 

 method of recognizing faults — of a peculiar type of cliff pro- 

 duced by faulting, which, though by no means obscure, had 

 previously been overlooked by geologists. It gave rise to a 

 new tentative explanation for the displacement of shore-line 

 discovered by barometer, namely, that it arose by faulting; and 

 it opened a new line of observation. 



Two hypotheses were now under consideration, but they 

 were not strictly alternative. Perhaps it would be better to say 

 that the origination of the second not only gave an alternative 

 but also modified the first. The Wasatch fault must affect the 

 height of the shore-line, and wherever it crossed the shore-line 

 that line must be discontinuous and exhihit two levels. The 

 admission of disturbance by faulting was therefore compulsory, 

 but faulting might or might not be sufficient alone. If it was 

 not sufficient, then undulation might complement it. The 

 modified first hypothesis was, undulation and faulting com- 

 bined, the second, faulting alone — both undulation and faulting 

 being themselves unexplained. 



It was not difficult to devise tests. An instrumental level 

 line might be carried along the old beach so as to ascertain 

 whether it rose or fell in regions where no faults occur; or its 



