240 W. H. HOBBS ORIGIN OF OCEAN BASINS 



Milne and Kikuchi.* Elevations as great as one inch per j^ear seem to 

 have been indicated, and the upward nature of the adjustment is abun- 

 dantly proven by the elevated sea terraces with coral reefs, f shell borings 

 in rocks, etcetera. 



There seems to be an increasing tendency to regard secular changes of 

 level as traceable to movements of the type which produce earthquakes — 

 that is to say, they occur not continuously, but per saltum. Exact meas- 

 urements have, however, not generally been made. The most valuable 

 exact data thus far available have been derived from the repetition of 

 trigonometrical surveys as soon as possible after a great earthquake. 

 At the time of the great Sumatra earthquake of 1892 a trigonometrical 

 survey was in progress, and a relocation of stations showed that actual 

 changes of position and elevation had occurred. J Much greater changes, 

 as regards both position and altitude, were determined to have occurred 

 during the great Indian earthquake of 1897, the relative changes of alti- 

 tude between stations being here as great as 24 feet and those of location 

 not less than 12 feet.§ Observations of a like character have been made 

 in connection with the earthquake of Saloniki in 1902. || The suggestion 

 of Issel that signals be established along the coast of Italy for the meas- 

 urement of bradysisms has been taken up by Grablowitz on the island of 

 Ischia. To extend the studies inland from the coast, Antonelli has 

 utilized with success a regular observation of the expanse of sea visible 

 below the horizon from a distant inland point, measuring the changes in 

 altitude against an intermediate building.^ That such a method could 

 be made available was known from the fact that certain villages in the 

 Jura which had been invisible 30 years before had come gradually into 

 view, the roofs first appearing and afterward a portion of the walls.** 

 Examples of a like nature have been given from Spain, Italy, Austria, 

 and Columbia, S. A.ff The proposition has recently been made to em- 



* John Milne : Movements of the earth's crust, etc. The Geographical Journal, 1896, 

 pp. 1-27. 



t Yoshiwara. 



t J. J. A. Mtiller : Ueber die Verschiebung elner triangulationsfeiler in der Residenz 

 Tapanuli (Sumatra) in folge des Erdbebens vom 17 Mai, 1892. Reviewed from Dutch 

 sources in Pet. Mitth., vol. 41, 1895, pp. 97-98. 



% R. D. Oldham : Report on the great earthquake of 12th June, 1897. Mem. Geol. 

 Surv. India, vol. 29, 1899, pp. xxx and 379, 44 pis. 



H Rud. Hoernes : Das Erdbeben von Saloniki am 5ten Juli, 1902, und der Zusammen- 

 hang der makedonischen Beben mit den tektonischen Vorgangen in der Rhodopemasse, 

 Mitth. d. Erdb.-Kom. d. k. Akad. d. Wiss. z. Wien, N. P. 



1[ G. Antonelli : Bradisismi di una parte della costa adriatica. Boll, della Soc. Geol. 

 Ital., vol. 9, 1890, pp. 119-131. 



**Glrardot: Notes sur les movements du sol qui se produisent actuellement dans le 

 Jura. Mem. de le soc. d'emul. du Doubs, 1881. 



tt Issel : Loc. cit., pp. 46, 105, 212, 258, 273, 354. 



