OciOBEB 25, 1907] 



SCIENCE 



557 



evidence of fault movement at all comparable 

 as to recency with the fresh scarps northerly 

 and southerly from the locality described. 



This fact and others of related significance 

 have inspired the prediction that the next or 

 at least a relatively early orogenic uplift in 

 this section of the Wasatch terrane will result 

 in a break to the east from Salt Lake City, 

 with accompaniments of destructive earth- 

 quakes.^ 



The foundation of this prophecy of assured 

 calamity has been questioned by the writer.' 



It is a fact that slight earth tremors occur 

 at frequent intervals in the Salt Lake Valley. 

 These tremors originate differently, mainly as 

 follows: (1) in orogenic slips incident to the 

 rise of the Wasatch mass, or, more precisely, 

 incident to the upward slip of some particular 

 section of the range, since the mountain mass 

 does not move as a whole; (2) in the slips in- 

 cident to the readjustment of the monoclinal 

 crust-blocks composing the Basin Ranges to 

 the west. These conditions of crustal move- 

 ment in this vicinity warrant the statement 

 that sesimographic records here obtained 

 promise results of both interest and value. 



The writer is pleased to report the installa- 

 tion of a pair of seismographic pendulums in 

 Utah. The apparatus as a whole may be 

 designated as the Omori-Bosch seismograph. 

 It was imported from Bosch, Strassburg. 



Before deciding on the purchase of this 

 type of apparatus, the writer inquired by cor- 

 respondence and personal visits as to instru- 

 ments for recording earth movements now in 

 operation in this country. The results showed 

 but few installations, and, according to the 

 reports, a considerable number of these were 

 of doubtful eiBciency. 



The Omori-Bosch seismograph includes a 

 weight of 100 kilograms suspended by a flex- 

 ible wire and supported in part by a cone and 

 socket attachment extending from an iron 

 column four and a half feet high, said column 

 being firmly anchored to a massive pillar 



" See Lake Bonneville, by G. K. Gilbert, Mono- 

 graph I., U. S. Geol. Surv., pp. 361, 362. 



' Scottish Geographical Magazine, September, 

 1902. 



rising from a deep foundation and isolated 

 from floor and other surface contact. At- 

 tached to the weight is a skeleton cone of 

 aluminum rods, which, with frictionless at- 

 tachments, operates a fine recording pen or 

 point. The tracing point rests on the surface 

 of a paper-covered revolving di'um. The paper 

 is glazed on one side, and when placed in posi- 

 tion on the drum is lightly smoked. 



A reliable contact clock is electrically con- 

 nected with the recording mechanism, and a 

 metallic point projecting from the armature 

 of an electro-magnet makest its imprint upon 

 the smoked paper at intervals of minutes or 

 seconds. The record during a period free 

 from earth tremors is a series of uninterrupted 

 lines with dots indicating time intervals; dis- 

 turbances are shown by cross tracings, of wide 

 amplitude and short duration when caused by 

 superficial jarring of the instrument, but 

 smaller as to amplitude, and otherwise dis- 

 tinctively different if caused by an earth 

 tremor reaching the pillar from below. 



The equipment at the University of Utah 

 comprises two instruments as described; these 

 are set respectively on the north-south and 

 east-west lines. One clock makes synchro- 

 nous record on each of the two drums. 



The sensitiveness of the apparatus is sur- 

 prising. A blast from the human lungs im- 

 pinging upon the side of the supporting pillar 

 is definitely recorded. A heavy hammer blow 

 on the end of the pillar, if delivered on the 

 line of the main axis — north-south or east- 

 west according to the pillar that is struck — • 

 makes no tracing beyond that due to a slight 

 upward jolt of the recording pen and the re- 

 turn of the point perhaps a little out of its 

 normal position. 



Each instrument is mounted on a pillar or 

 pier of concrete, extending about 15 feet be- 

 low the floor. The entire apparatus is en- 

 closed within a tight case with glass sides. 



On July 2 a powder explosion occurred 

 about three miles from the university grounds. 

 The explosive was fired while packed in 

 freight cars awaiting removal to the magazine 

 buildings near by. According to report 725 

 kegs of blasting powder and a ton of giant 



