220 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



In the region of the Bahamas, according to A. Agassiz, subsidence has 

 been progressing during epochs which correspond with these regional 

 uphfts in the Antilles. 



The uniformity of this epeirogenic movement is also broken at two 

 places by synchronous orogenic deformation : on the Leeward side of the 

 AVindward Islands, where the modern reef rock is found 300 feet above 

 the sea in disturbed patches, and at Port Limon, Costa Rica, where the 

 Pleistocene beds are deformed. Furthermore, at the eastern extremity 

 of the region, the island of Barbados, the Post-Pleistocene uplift is en- 

 tirely discordant with that of all the rest of the region, the coral reefs of 

 Barbados having risen to an altitude of 1.100 feet. 



Synclironously with the rising of the reef, volcanic piling has continued 

 on the mainland and in the Windward Islands, although the mass of 

 ejecta duriug these later days is Lilliputian in comparison with the great 

 heaps of debris piled up in preceding epochs. The present craters and 

 vents of the Mexican, Costa Eican, and Windward summits are mere ant- 

 hills capping the older mountains of ejecta. The last volcanic fires of the 

 Cordilleran region of northern Mexico and the United States expired in 

 Pleistocene time. 



The differing altitudes of the synchronous elevated reefs teach some 

 important lessons. On close analysis they show that the apparent uni- 

 formity of uplift does not persist, and resolves itself into a wide, swell- 

 like movement, with different intensities in various parts of the field, 

 gradually decreasing towards the United States, where hitherto Post- 

 Pleistocene movements of the West Indies and the continent had been 

 considered so uniformly continuous. These inequalities in the Post- 

 Pleistocene uplifts of the West Indies also controvert the position main- 

 tained that the elevated terraces might be due to shrinkage of the sea 

 rather than elevation of its bottom. 



The data presented are insufficient to show enough expansion of the 

 West Indian lands in Post-Oligocene times to have connected the islands 

 with the mainland or with one another, or to have created a continuous 

 Windward bridge, as has been alleged. 



Resum^. 



With the data presented, we can now briefly review the major pro- 

 cesses of diastrophism which have produced these great changes of level 

 in the Tropical region in later Mesozoic and Cenozoic times, and their 

 effects u];^n the configuration of the lands. 



