650 WM. HERBERT HOBBS 



by Fuller's account of the Jamaican earthquake of January 14, 1907.' 

 A cement culvert at the mouth of a stream was buckled up and 

 broken through the movement of its walls toward the center of the 

 valley (see Fig. 4, D). 



It is believed that the above data are sufficiently full and decisive 

 to warrant the conclusion that during a destructive earthquake the 

 banks of valleys generally draw together so as to shorten the inter- 

 vening distance. The examples of deformed bridges which have 

 been offered in evidence, have not been selected for the purpose of 

 proving a point, but include all which have come to the writer's atten- 

 tion. The unique exception to the law which otherwise controls, is 

 furnished by the railway bridge over the Pajaro River damaged during 

 the California earthquake of 1906; and, inasmuch as this bridge lies 

 across the rift line at an acute angle it seems likely that special shear- 

 ing movements along the rift plane have here been of larger measure 

 than the normal contraction of the valley. 



It appears, further, to be a fact of general observation, that a 

 fissure or series of parallel fissures open during earthquakes along the 

 banks of rivers parallel to their courses (see Fig. T),C). According to 

 Milne^ within the Aichi prefecture in Japan, after the earthquake of 

 1 89 1, more than four hundred miles of river banks, water trenches, 

 and roads were found destroyed through action of this kind. On 

 river banks the fissured zone and hummocky ground looked as though 

 gigantic plows had torn out furrows several feet in width and some- 

 times as much as twenty feet in depth, and this character of the 

 surface extended from ten to fifty yards from the river. Such struc- 

 tures can be only in part explained through the shaking down of loose 

 material such as is found in a railway embankment on which the tracks 

 approach bridges, for the reason that such mere removal of support to 

 rails should give the effect of tension rather than compression. 



Thomas Oldham, who first seriously studied the fissured river 

 banks in connection with the Cachar (Indian) earthquake of January 

 10, 1869,3 went out from the conception of an earthquake centrum 



1 M. L. Fuller, "Notes on the Jamaica Earthquake," Jour. Geol., Vol. XV, 1907, 

 pp. 718, 719. 



2 John Milne, Seismology, p. 148. 



3 Quart. Jour. Geol. Soc. Lond., Vol. XXVIII (1872), p. 255. See also Mem. 

 Geol. Surv. India, Vol. XIX, Pt. i, pp. 52-56, PL vi. 



