DIASTROPHISM AND THE FORMATIVE PROCESSES 141 



Nicobar Islands in this tract are isolated much as are the Wind- 

 ward Islands, and bear deposits interpreted as oceanic. 



It appears therefore that all the more notable cases of this class 

 are situated on hinge-line areas where notable flexures of the shell 

 have been pronounced features, and where all movements are 

 perhaps to be regarded as of a special order rather than as typical. 



If we grant that all these are cases in which the crust has really 

 oscillated from abysmal depths to atmospheric levels, they can 

 scarcely be said to affect seriously the broad conclusion of per- 

 manency of the true continents and ocean basins drawn from the 

 absence of abysmal deposits in the continental terranes, and from 

 the probable presence of these beneath the recent accumulations 

 on the abysmal segments. 



Returning to the Barbados case, the gist of the local problem is 

 found in (i) a lower deposit unquestionably formed in shallow 

 water, (2) a middle "oceanic deposit," consisting of some beds 

 resembling globigerina ooze and of others resembling radiolarian 

 ooze and "Red Clay" — -the group thought to imply a depression 

 to 10,000 or 12,000 feet — and (3) an upper stratum of coralline 

 rock, implying a return to shallow waters, and later (4) an eleva- 

 tion of 1,100 feet above the sea. The series has been made the 

 subject of an elaborate study by A. J. Jukes-Brown and J. B. Harri- 

 son,^ and of shorter papers by G. F. Franks and J, B. Harrison,^ 

 J. W. Gregory,^ and J. W. Spencer.'' The chemical, physical, 

 and biological comparisons of Jukes-Brown and Harrison make 

 distinctly plausible an abysmal descent between the formation of 

 (i) and the formation of (3), during which the oceanic beds were 

 laid down. The island stands by itself and was completely sub- 

 merged; its uppermost parts are mantled by the oceanic deposit. 



' A. J. Jukes-Brown and J. B. Harrison, "The Geology of the Barbados," Quart. 

 Jour. Geol. Soc. London, XL VII (1891), 197-250; XLVIII (1892), 170-226. 



2 G. F. Franks and J. B. Harrison, "The Globigerina Marls and Basal Reef-Rocks 

 of Barbados," ihid., LIV (1898), 540-55. 



5 J. W. Gregory, "Contributions to the Paleontology and Physical Geology of the 

 West Indies," ibid., LI (1895), 255-310. 



4 J. W. Spencer, "On the Geological and Physical Development of Barbados with 

 Note on Trinidad," ihid., LVIII (1912), 354-67. 



