160 bulletin: museum of comparative zoology. 



shape. This constituted a gently arched openly folded anticlinal struc- 

 ture, inclining north and south. This broad fold is marked in its 

 course by numerous short secondary wrinkles or miniature low anticlinal 

 folds, as is so beautifully shown in many places, notably near Catadupa 

 and Montpelier. (See Figs. 18, 19, 20.) 



Accompanying this uplift was a great intrusion from below of the deep 

 seated granitoid and dioritic rocks we have described. The central 

 location of this mass below the limestone, now so beautifully exposed 

 by subsequent erosion in St. IMary, the metamorphism which the over- 

 lying Montpelier beds have suffered, and the numerous dikes protruding 

 from it through the oceanic limestones and Blue Mountain Series, indi- 

 cate that this laccolith was contemporaneous with this epoch, and cor- 

 roborate the belief that, if it was not the direct cause, it was at least 

 intimately associated with this Mid-Tertiary (Oligocene'?) uplift of 

 Jamaica. 



The higher terraces or levels, between 1,000 and 2,100 feet, seem to 

 have been during or immediately following this emergence epoch, and 

 previous to the next subsidence ,to be described. We shall also show 

 that this event was not peculiarly Jamaican in its effects, but had a 

 wide reaching influence in Antillean and Central American geography. 



The next event in Jamaican history was a renewal of subsidence and 

 a contraction of the land to its present back coast borders. This sub- 

 sidence, recorded in the Bowden formation, involved at its conclusion 

 only the margins of the present island area, which at its beginning was 

 probably expanded beyond its present borders. It was initiated by the 

 deposition of the land derived littorals of Bowden gravels, found only 

 in the north and south coasts of the eastern portions of the island, and 

 probably culminated in the deposits of the shallow marls. The ampli- 

 tude of this movement was jirobably less than one third that of the 

 great Montpelier subsidence. The Bowden and Cobre beds encrust 

 the pediments of the island up to a height of less than 300 feet. The 

 land area during this epoch again became insular in character.^ 



Succeeding the Bowden epoch there was another upward movement 

 of the island. The larger portion, which had remained land during the 

 Bowden subsidence, including much of the Limestone Plateau and the 



1 The probable absence of these formations from the western lialf of the island, 

 if true, and the immediate east coast if proven after further research, may indicate 

 that tlic Janiaica-IIaiti land connection continued to exist during their deposition, 

 and that the more extensive lands existed to the south and west in the vicinity of 

 the Pedro Banks or beyond. 



