HILL: GEOLOGY OF JAMAICA. 219 
tho Bahamas, the west side of the Caribbee volcanic chain, and perhaps 
. the islands and coast of the north side of Venezuela, showing the wide 
extent of the recent epeirogenic uplifts. The elevated reefs of the West 
Indies, especially those forming the Great Antilles, are all manifestations 
of this event. On the mainland of Florida, Texas, Yucatan, and Panama, 
it is recorded in the elevated position of synchronous Post-Pliocene for- 
mations of diverse material above sea level. Many small isolated islets, 
like Barbuda, Desirade, Marie Galante, and Basse Terre of Guadeloupe, 
making the eastern limit of the Windward Islands, with their double 
benches, show their wide extent in that direction. Other isolated dis- 
connected islets, like Navassa, southeast of Haiti and Alta Viela, show 
the same unmistakable record in their benched topography. 
All these recently elevated benches are not reef rock, but many of 
them are wave-ent terraces. In Barbuda, for instance, they are com- 
posed of old beach and shallow littoral débris, now cemented into lime- 
stone, as are many of the Florida Keys described by A. Agassiz. It 
may be that the higher summits of the low benched islands of the 
Barbuda and Navassa type are remnants of the oldest Post-Plio- 
cene elevation, and that the lower terraces record a later Pleistocene 
uplift. 
Whether constructional benches of elevated reef rock or wave-out 
éliffs and terraces, these phenomena are all manifestations of the same 
general uplift that has taken place in Tropical America since the Plio- 
cene subsidence we have described. 
The known data of the wide area of these Pleistocene and later up- 
lifts, as uniform as they appear, present some interesting facts showing 
important differential movements. These are characterized by wide ex- 
tent and small amplitude. The region of greatest uplift, excepting Bar- 
bados, is adjacent to the Windward passage, where a maximum of at 
least 600 fect is recorded. From this locality the amplitude decreases 
north, south, and west, the elevation being only a few feet at Colon and 
in southern Florida. To the south of east as far as Barbuda and 
Desirade cast of Guadeloupe, the amplitude maintains an altitude of 
over 125 feet, indicating that the uplift was a very gentle oval swell, 
having an east and west axis. From Barbuda to Colon is about twenty 
degrees of longitude, or over 1,300 miles, and at the extremes and mid- 
dle of this line there are stations by which the differentiation of the 
movement can be determined, and these show that considerable differ- 
ences exist. At Barbuda the highest bench is 125 feet; at Navassa in 
the centre, 250 feet ; at Colon on the west, five feet. 
