OCEAN BASINS OF THE SECONDARY ERA 241 



ploy photography to record such movements.* After the selection of a 

 station with widely extended view (if possible, where several mountain 

 ranges are visible at successively greater distances), photographs are to be 

 taken with powerful telephoto-lenses at fairly regular and frequent inter- 

 vals and under as nearly as possible the same atmospheric conditions. 

 Such records, if made at a sufficiently large number of stations, can 

 hardly fail to give a decisive answer to the question whether the so-called 

 secular movements are in general continuous and regular or spasmodic 

 and occasional; and, if the latter, whether the time of the change corre- 

 sponds to local felt earthquakes or to periods of earth rumbling unac- 

 companied by sensible movement. 



The Ocean Basins of the Secondary Era 



A great contribution to our knowledge of ocean basins has been made 

 by Haug, who, by bringing together the data of zoologists and botanists 

 and placing them in relation to the results obtained by stratigraphic geol- 

 ogists, has shown that the great zone of geosynclinals — the belts within 

 which the geological record is most nearly complete for the Secondary 

 era, and which must therefore have then constituted the almost contin- 

 uous sea-basin — these geos3'^nclinals bound the zoogeographic and botano- 

 geographic provinces of pre-Tertiary time.f Suess showed long agoj 

 that the faunas of the geos)riiclinals have more generally a pelagic 

 character. 



The recent study of earthquakes has shed new light from more than 

 one direction upon the problem of ocean basins. By the study of a life- 

 time the Count de Montessus has been able to show through a process of 

 standardization and correlation that practically all the recorded earth- 

 quakes of the land areas (about 170,000 in number) have been localized 

 within two great-circle belts of the globe, and that these belts correspond 

 in position to the geosynclinals as they had already been mapped by 

 Haug.§ These belts are today the highest regions and bordered by the 

 steepest slopes on the land ; and, though the continuous or nearly con- 

 tinuous low depressions of the Secondary era, they became the mountains 

 of the era which followed. They are thus regions which have been 

 most mobile during and since the Tertiary, and their present importance 



* G. Agamennone : Determination des bradysismes dans I'interieur des continents au 

 moyen de la photographie. Bull, de la soc. beige de geologie, vol. 18, 1904, pp. 20-38. 



t fimile Haug : Les g^osynclinaux et les aires continentales. Bull. Soc. Geol. France. 

 3d ser., vol. 28, 1900, pp. 617-711. See also .Jour. Geol., vol. 15, 1007, pp. 294-297. 



t Ed. Suess : Bntstehung der Alpen, 1875, p. 98. 



§ Loc. cit, p. 633. 



