HILL: GEOLOGY OF JAMAICA. 107 
The Post-Bowden (Miocene) emergence equalled the combined thick- 
hess 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 places. 
The amplitude of the Pliocene subsidence, if there was one, judged 
from the thickness 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 
‘sland to its present insular condition. 
The Pleistocenc-recent emergence in Jamaica can be measured by the 
Position of the top of the emerged Pliocene rocks above the 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 mero guesses. 
The number and amplitude of these great oscillations, and the radical 
“evolutions 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- 
tama of gigantic changes. Yet there is reason to believe that these 
Novements were not catastrophic in character, but of that dignity which 
companies all the great isostatic changes. They are merely further 
illustrations that geologic time is long, notwithstanding our incapacity 
r 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 
Ppa which participated in them, and of which it is the geographic 
entre, 
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