272 HOBBS— THE EVOLUTION AND THE [April 24. 



intensity of shocks, (2) whether these are repeatedly the seat of 

 special danger from successive earthquakes, and (3) whether such 

 lines, if they exist, are expressed in the surface of the country as 

 earth lineaments. The investigation showed that at the time of an 

 earthquake the surface of the country affected is peculiarly sensi- 

 tized to reveal the courses of hidden faults, which, if thus made 

 apparent, may be designated seismotectonic lines, and that strong 

 seismotectonic lines correspond in position to the striking linea- 

 ments of the country. In this we find a means of deriving through 

 the study of the topography, the tectonic geology and the seismic 

 history, an imperfect yet none the less a valuable map to display 

 the architecture of each seismic district. 



It is a curious illustration of earlier misdirection of effort, that 

 up to the year 1907 no detailed map of the fault system within an 

 area disturbed by destructive earthquake had been attempted. The 

 maps which best display the disposition of adjusted fault blocks 

 were the small-scale charts by Thoroddsen and by Tarr and Martin. 

 In the summer of 1907, at the writer's suggestion, the expert topog- 

 rapher and geologist, Mr. W. D. Johnson, of the U. S. Geological 

 Survey, prepared accurate maps of the surface faults of certain 

 areas disturbed during the Owen's Valley earthquakes of 1872, 

 which maps were published in part during the same year.^^ The 

 sudden changes of displacement on individual faults and the mosaic- 

 like structure of the disturbed region were thus brought out with a 

 clearness and accuracy never before attained. 



Seismological science may be said to have suitably celebrated its 

 emancipation from the bondage of the centrum theory, when in 1907 

 there was published from the pen of the Count de Montessus de 

 Ballore the most comprehensive treatise upon the subject.^®^ This 

 book recognized the adjusted fault block theory as the best avail- 

 able working hypothesis of the science, and with a grasp of the 

 subject which was based upon a lifetime of study, and upon a quite 

 unparalleled knowledge of the literature, earthquakes were so treated 

 as to make the work the one authoritative reference book of the 

 science. 



" In the author's " Earthquakes," Figs. 23, 45 and 64. More complete 

 maps will appear in a special monograph. 



"* La Science Seismologique, Paris, 1907, pp. 579. 



