hill: geology of JAMAICA. 107 



The Post-Eowdcn (Miocene) emergence equalled the combined thick- 

 ness of the Bowden beds, the depth of deposition and their present 

 altitude above sea level of about 300 feet, or a total not exceeding 

 1,000 feet. This movement was to a certain extent orogenic, resulting 

 in deformation by tilting and differential elevation, the rocks being 

 inclined as high as twenty degrees in ^jlaces. 



The amplitude of the Pliocene subsidence, if there was one, judged 

 from the tliickness of the Pliocene deposits, could not have exceeded 

 the interval between the present 100 foot contour of the land to about 

 the 100 fathom line of the sea, or a total of 700 feet. It was probably 

 much less. This was sufficient, however, to restrict completely the 

 island to its present insular condition. 



The Pleistocene-recent emergence in Jamaica can be measured by the 

 position of the top of the emerged Pliocene rocks above tlie sea (200 

 feet), and a conjectural supposition that they were deposited at a depth 

 of over 100 fathoms, or a total of at least 800 feet. 



The foregoing estimates platted upon the diagram (Figure 40) are not 

 given with any idea of finality, but as a preliminary contribution — the 

 mere entering wedge — to a subject which future studies will improve, 

 amplify, and correct. They sufficiently approximate the truth to be 

 considered of greater value than mere guesses. 



The number and amplitude of these great oscillations, and the radical 

 revolutions in geography which they produced, not only appal the mind 

 by their magnitude, but have taken place with rapidity, — all having 

 practically occurred in the Cenozoic era. They present a flashing pano- 

 rama of gigantic changes. Yet there is reason to believe that these 

 movements were not catastrophic in character, but of that dignity which 

 accompanies all the great isostatic changes. They are merely fm-ther 

 illustrations that geologic time is long, notwithstanding our incapacity 

 for conceiving the fact. 



The amplitude of each of these movements, if known with exactness, 

 would be an important key note not only to Jamaican history, but also 

 would throw important light upon the whole of the Tropical American 

 region which participated in them, and of which it is the geographic 

 centre. 



