1897-98]- LATE FORMATIONS AND GREAT CHANGES OF LEVEL IN JAMAICA. 



337 



base levels of erosion (see Map, page 328 and Figure 4). The deeper 

 channels belong to a later date. This resemblance suggests that the 

 submarine plateau with embayments reaching into the insular mass 

 of Jamaica, such as that south of Kingston, was a land surface during 

 the Mio-Pliocene elevation. The abrupt descent of the northern side 

 of the island suggests great dislocations off that part of Jamaica, and 

 that the forces which squeezed up the island, also rammed down 

 the sea floor to the north. However, it must be emphasized that 

 all the disturbing forces whether acting on what are now land sur- 

 faces or those submerged have not generally obliterated the ancient 



Figure 4. — Map showing the character of the embayments off Kingston Harbor ; and the coastal 



plains back of the city. 



drainage. It may be noticed that the writer assumes that typical 

 valleys with open drainage are the result of atmospheric denudation. 

 This problem has been discussed in both the " Reconstruction of the 

 Antillean Continent," and in the "Geographical Evolution of Cuba."* 

 It will be again referred to in succeeding pages after describing the 

 local characteristics of the different geological periods, as the physical 

 features of Jamaica have their counterparts on the other islands. 



*By J. W. Spencer, Bull. Geol. Soc, Am., vol. vii., pp. 10^14°. '894 : ^"^ '*'■ ^'i'''- ^'"- PP- 67-94' '8qS- 



