242 W. H. HOBBS ORIGIN OF OCEAN BASINS 



as earthquake regions indicate that the cycle of change is uncompleted. 

 This revelation, that the Tertiary was for later geological history not 

 only the unique period for mountain birth and growth and for lava ex- 

 travasation, but also for the formation of new ocean basins as well, has 

 shown that some sort of balance was maintained between areas elevated 

 in one part of the globe and those depressed in another. 



Distribution op Seaquakes and Tsunamis 



A noteworthy contribution to our knowledge of the ocean basins is to 

 be found in the comprehensive study by Kudolph* from direct observa- 

 tions of seaquakes, submarine volcanic eruptions, and "tidal waves." f 

 After search in earthquake catalogues, nautical magazines, ships' logs, 

 etcetera, he has described and charted the observations of mariners re- 

 garding the quakings experienced upon vessels and likewise the under- 

 sea eruptions. These data from untrained observers are surprisingly 

 accordant, which speaks for their general correctness. It is learned, 

 and this is an observation of the greatest value, that the sensible shake 

 from a submarine quake is soon lost in transmission through the sea, as 

 is clearly shown by the fact that of two ships an angular degree apart one 

 has received a very violent shock, though it has passed the other un- 

 noticed. This observation, confirmed by the study of the explosions of 

 submarine mines, gives great value to the observations, which are defi- 

 nitely located in position by the ships' logs. In a number of instances 

 the alignment of shaken vessels has been apparent, as in the seaquake of 

 December 22, 1884, which was located near the Azores. 



Eegarding the origin of under-sea disturbances Rudolph says : 



"Movemeuts of the iudividual parts of a fault cleft upou each other, be it iu 

 vertical or horizontal direction, are inconceivable without shaking of the oro- 

 graphic blocks (ScliolJen). It is a peculiarity of these tectonic earthquakes 

 (one may call them dislocation or structure quakes, or. if you will, he may 

 still further distinguish Blatt and Wechsel quakes) that with slight lateral ex- 

 tension of the shaken plane they are transmitted in a definite direction coin- 

 ciding with the cleft" (p. 277). 



The map of the globe on which Rudolph has charted his results]; shows 

 a confirmation of the correctness of the map of macroseismic origins by 

 Milne on the one hand and with de Montessus's map of the regions of 

 high seismicity on the other. The tsunamis as charted by Rudolph fringe 



* E. Rudolph : Ileber submarine Rrdbeben und Bruptionen. Beitrage z. Geophysib, 

 vol. 1, 1887, pp. 133-365, pis. iv-vli ; vol. 2, 1895, pp. 537-666 ; vol. 3, 1898, pp. 273-336. 



t We .shall adopt the excellent .Japanese term tsunamis for these earthquake waves so 

 generally and erroneously denominated tidal waves. 



t Loc. cit., vol. 1, pi. vii. 



