hill: geology of JAMAICA. 199 



diastrophism, orogeny, and physical geography, must all be considered. 

 The past and present distribution of life of all orders, both land and 

 marine, their paleontologic history, the part which the debris of their 

 skeletons, extracted from the liquid sea, has played in accumulating 

 strata upon the submerged slopes and bottoms or building coral reefs 

 are also important factors. The possibilities of the great Equatorial 

 current and Gulf Stream, as carriers of sediment, corrosive agents, and 

 the effect on the distribution of lime-making organisms is also a most 

 important consideration. 



There are several important conditions which make all attempts at 

 final interpretation of Antillean and Tropical American history more or 

 less hypothetical. The first of these is the fact that the submarine con- 

 figuration suggests that large areas of land now submerged may have 

 existed, not only in the immediate basins of the American Mediteiranean, 

 but also in the Atlantic and Pacific waters off the present continental 

 borders. These submerged areas are now so covered with accumulations 

 of organic and oceanic debris that their geologic composition can never 

 be approximated even by soundings. Much of the older sedimentary 

 strata of the present land masses have also been as completely concealed 

 by burial beneath vast accumulations of volcanic ejecta, especially in 

 Central America, the southern end of the Mexican Plateau, and the 

 Caribbee Islands. 



Notwithstanding the incompleteness of the record, the general con- 

 figuration, and the geologic structure and paleontology of the land areas, 

 and the distribution of the present life of the land and sea, afford much 

 data of a fragmentary nature which can be so placed together as to throw 

 some light upon the geologic evolution of the region. The discussion of 

 the biologic and hydrographic phases of the question must be left to 

 others, and in this chapter only the testimony of the structural geology 

 and the configuration will be discussed. 



The geologic composition and arrangement of the rock sheets relative 

 to one another record in a manner changes of level, relative depth of 

 deposition, and position of land areas. Variations in the physical and 

 chemical composition of strata, when traced over wide areas, enable us to 

 judge with a degree of conjecture the location of the land from which 

 they were derived or the extent of their basins of deposition, and to con- 

 struct hypotheses of former bathymetric variations. Features of land 

 configuration by which events of elevation, degradation, and subsidence 

 can be traced, should present harmonious and parallel conclusions 

 with the interpretation of the fossils and the strata. Many writers of 



