270 HOBBS— THE EVOLUTION AND THE [April 24. 



earth's crust. Since the formation of this cleft, which is at least of pre- 

 Cretaceous age, doubtless movements have often occurred which continue 

 even to our time. . . . 



In the following year the Count de Montessus de Ballore, who 

 had already become known as a seismologist of reputation by reason 

 of his masterly essay upon the distribution of seismicity over the 

 globe, brought out a comprehensive work entitled " Seismic Geog- 

 raphy." In this volume, as a result of the study of no less than 

 170,000 recorded shocks of earthquake, their distribution within 

 each province was analyzed by new and ingenious methods of com- 

 bination. In each case the known faults of the district under con- 

 sideration were discussed, and so far as possible, their relation to 

 the seismic distribution was brought out.^* 



Much the clearest demonstration of the adjustment of por- 

 tions of the earth's crust as individual blocks, and here by well- 

 demonstrated changes of level, is to be found in a paper by Tarr 

 and Martin upon the results of earthquakes in' Alaska in the fall 

 of 1899.^^ Some portions of the coast were found to have been 

 elevated, and other smaller ones to have been depressed. The sea, 

 which here cuts up the district by a number of fiords, permitted the 

 changes of level to be measured by the height of the abandoned 

 shore lines of 1899. In the absence of earlier soundings or of cor- 

 rect maps, the submerged areas were determined with much less 

 precision, though forests now below sea level bear abundant testi- 

 mony to the local direction of the earth movement. Still older 

 abandoned shore lines, appearing as notches above the raised beach 

 of 1899, proved that the latest elevation is but one stage in the 

 progressive, though interrupted, general uplift of the region. Tarr 

 and Martin's statement of their view is as follows : 



Briefly summarizing the inferences which the facts seem to warrant, we 

 conclude that in 1899 there was a renewal of mountain growth, uplifting 

 that part of the mountain front bordering the Yakutat bay inlet to different 

 amounts — 7 to 10 feet in the southeast side of the bay, and 40 to 47 feet on 

 the northwest side. This uplift occurred all within a little over two weeks 

 and mainly on a single day (September 10). It was complicated by move- 



" " Les tremblements de terre ; Geographie seismologique," Paris, 1906, 



pp. 475- 



^° " Recent Changes of Level in the Yakutat Bay Region, Alaska," Bull. 

 Geol. Soc. Am., Vol. 17, 1906, pp. 29-64, pis. 12-23. 



