hill: geology of Jamaica. 219 



the 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-cut terraces. In Barbuda, for instance, they are com- 

 posed of old beach and shallow littoral debris, 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 N^avassa 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-cut 

 cliffs 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 Mide 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 feet 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 east 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 j at Navassa in 

 the centre, 250 feet ; at Colon on the west, five feet. 



