40 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY, 
the southern part of St. James ; Cutting-Grass-Spots and Dean's Rivers, 
Westmoreland ; and Content River in Hanover. It is supposed that the 
waters of these streams, after sinking into the ground, in some instances 
find underground connection along the contact of the Blue Mountain 
and White Limestone Series and into the coastal streams, In many 
cases the head waters of the marginal streams have captured the drainage 
of the great interior basin valleys, especially the Minho, Cobre, Montego, 
Black River, and Great River. This is shown by the fact that the 
middle portion of these streams, where they cut the White Limestone 
Ridge between the plains and the central valleys, have newly formed V- 
shaped canyons containing no alluvial material such as occurs in the 
interior valleys which they drain and the lower Coastal Plains through 
which they flow. The topography of Bog Walk Canyon, shown on 
Plate X., illustrates the character of the more newly made, interme- 
diate, connective portions of this compound type of streams. 
Without details of the geologie structure, it is evident from this 
topographie review that the present land features of Jamaica are of 
complex origin, and record many past events of uplift and subsidence 
which have produced different phases of configuration and outline at 
different epochs of its history. 
Summarized, this history involves: — 
(1) Two periods of mountain making (including the elevation of the 
plateau in this category) accompanied by greater expansion of the 
island than its present area. The first of these has prevalent north of 
west trends; those of the second are east and west. The profiles of the 
former are angular, of the latter gently arched. 
(2) Two great epochs of subsidence and contraction of the land, 
alternating with periods of elevation. 
(3) Later uniform elevation which added the narrow modern coastal 
phenomena. 
Finally, we may add that the configuration of Jamaica does not 
cense at sea level, but there is every evidence that the visible portion of 
the island is only the tip of a more extensive foundation below the 
level of the sea, which, especially to the south and east, presents 
terraced features somewhat similar to those of the exposed coast borders, 
and which indieate that once the island was slightly more extensive 
than at present. 
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