March 15, 1895.] 



SCIENCE. 



293 



Humboldt. Helinert. Penck. 



F^uropc, 

 Asia, 

 AfKca, 

 Australia, 



20.5 

 351 



300 330 m. 



500 1010 



500 (i()0 



2.50 310 



Xorth, 22S ) .,^ 



America, '"V,"' ^T,. '; -'85 410 ^'i^. ] 650 

 houth, 34() ) boO j 



All Continents. 30S 440 735 



Tlie increase in tlie values of the latter 

 measures is probablj' an approacli to the 

 truth, for early explorations frequently gave 

 too much emphasis to narrow mountain 

 ranges, and too little to broad plateaus. 



A. AGASSIZ OS THE BAHAMAS. 



A EECOXNOissANCE of the Bahamas and of 

 the elevated reefs of Cuba, made by A. 

 Agassiz in the winter of 1893, affords 

 material for a Bulletin of 200 pages with 47 

 plates and many figures in the text, lately 

 issued by the Museum of Comparative Zo- 

 ology at Harvard College. The author is 

 emphatic in rejecting the sufficiency of the 

 Darwin-Dana theory of submergence in ex- 

 plaining the features of great limestone 

 banks. The Bahamas consist of low hills 

 of leolian limestone, " formed during a period 

 of rest, during which the great beach of the 

 then existing reef constantly supplied fresh 

 material to be changed by the surf and the 

 winds into sand for the heaping up of sand 

 dunes. They could not be formed in a dis- 

 trict of subsidence unless the subsidence was 

 slower than the rate of growth of the corals, 

 which is not the case in the Bahamas, as the 

 reefs of to-day, even when they come to the 

 surface, are not tlie sources from which the 

 material for the great dunes of the Bahama 

 Islands is derived " (p. 184, 185). At pres- 

 ent the dunes are disappearing before the 

 action of the sea. The conclusion of the re- 

 connoissance seems to be that the great 

 limestone banks are chiefly formed as 

 ' marine limestones,' accumulating ' at great 

 depths by accretion ; ' and that in the AVest 

 Indies " wherever coral reefs occui-, and of 



whatever shape, they form onlj' a compara- 

 tively thin growth upon the underlying 

 base" (p. 177). The text, with its figures, 

 supjjlemented by maps and plates, gives an 

 excellent idea of the geographical features 

 of the region and of their evolution. 



spencer's eecoxsteuction of the antil- 

 leax contixext. 



Prof. ]\Iarcel Bertraxd, of the Ecole 

 des Mines and the Geological Survey of 

 France, has published an account of certain 

 faint deformations of northwestern France, 

 in which he interprets the inequalities in 

 the floor of the Englisli channel as the re- 

 sult of faint anticlinal and synclinal move- 

 ments (Bull. Soc. Geol. France, xx., 1892, 

 118); thus implying that neither erosion 

 nor deposition has been of significant meas- 

 ure in shaping the channel floor. Prof. J. 

 W. Spencer takes almost the other extreme, 

 and interprets certain inequalities of the 

 ocean floor of the Antillean region, even to 

 depths of twelve or fifteen thousand feet, as 

 the results of river erosion during a not re- 

 mote time when the entire region is sup- 

 posed to have had a much greater altitude 

 than at present (Bull. Geol. Soc. Amer., vi., 

 1895, 103-140); thus implying that no 

 other processes than river erosion can ac- 

 count for the inequalities that he has traced. 

 It must be concluded from these contrasted 

 arguments that the forms of the sea floor 

 are not yet so well understood as those of 

 the land ; because the facts are much less 

 accurately known under than over sea level, 

 because only form and not structure can be 

 determined by soundings, and because the 

 forms of the sea floor have received rela- 

 tively little study. "Where two specialists 

 reach conclusions so unlike, it is difficult 

 for others to choose l)etween them ; and for 

 the present there will probably be some 

 hesitation in adopting the teachings of the 

 one or the other. "With much interest 

 aroused in the facts brought forward, and 



