Vol. 57.] PHYSICAL DEVELOPMENT OF ANTIGUA. 505 



activity has prevailed, but this is a question for consideration when 

 studying the general changes of level of the Antillean plateau. 



The Miocene-Pliocene elevation in Antigua was followed by a sub- 

 mergence (the Friar's Hill) to a depth of 200 feet below the 

 present altitude. On this account it is possible that the mechanical 

 accumulations of Antigua are represented in Barbuda by calcareous 

 beds containing a recent type of organic remains. 



Polio wing this submergence about the close of the Pliocene 

 Period, the land rose to a great altitude. The evidence from the 

 dissection of the banks shows the elevation to have reached 2000 

 feet. But the submarine plateau between Antigua and Guadeloupe 

 is further incised by channels, indicating tKe elevation to have 

 exceeded 3000 feet. This is not the extreme height to which 

 the region rose, but the evidence lies beyond the province of this 

 paper. These conditions did not continue sufficiently long to 

 complete the dissection of the tablelands, and consequently the 

 Antigua-Barbuda mass remains intact. This elevation (subsequent 

 to the deposition of the Friar's Hill Series) was in the early 

 part of the Pleistocene Period, fuller evidence of which occurs 

 elsewhere.^ 



Then followed a subsidence, which culminated in a submergence 

 to a depth of 75 feet when the Cassada-Garden Gravels were 

 deposited, to be succeeded by a re-elevation — not merely to this 

 amount, but to 100 feet or more — when the shallow channels on 

 the submarine bank were formed. This feature would be in 

 harmony with the later movements observed in other islands. 

 Sufficient study has not been given to the subject to determine 

 whether the recent marls on the eastern coast were laid down 

 during the post-Cassada Garden emergence — in which case they 

 were once considerably higher before sinking to the present level — 

 or whether they belonged to a later episode indicating another 

 subsidence and re-emergence to a height of 10 feet. However, a 

 doubt is cast upon a very recent re-emergence, on account of the 

 considerable age of the shells in the marls, and also because 

 recent corals do not occur in the raised reefs. 



EXPLANATION OF PLATE XV. 



Geological sketch-map of the Island of Antigua, on the scale of about 2^ miles 

 to the inch. 



A south-western mountain-zone composed of old igneous formations ; a central 

 rolling valley-belt with undulating hills, formed of tufaceous deposits ; 

 a north-eastern hilly or rolling country underlain by early Tertiary 

 (Eocene-Oligocene) White Limestones, whose eroded surfaces are often 

 succeeded by a denuded mantle of the Friar's Hill Series of marls. 

 There are also isolated patches of a later formation of gravel, as at Cassada 

 Garden. 



1 See ' Reconstruction of the Antillean Continent,' Bull. Geol. Soc. Am. vol. vi 

 (1895) pp. 103-40; 'Geographical Evolution of Cuba,' ibid. vol. vii (189(5) 

 pp. 67-94; and 'Late Formations & Great Changes of Level in Jumaicsa,' 

 Trana. Canad. Inst. vol. v (1898) pp. 325-58. 



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