1897-98]- LATE FORMATIONS AND GREAT CHANGES OF LEVEL IN JAMAICA. 33I 



The succeeding '' Yellow Limestone Formation " consists of yellow 

 sands, and marls with layers of limestone. In the middle part of the 

 series, the marls are replaced by Orbitoidal limestones. This formation 

 has been classed as of Miocene age, but the presence of Orbitoides 

 correlates it with the Eocene of the northern continent. Moreover, at 

 the base of the overlying " White Limestone," fossils have been col- 

 lected belonging to the Eocene period. Above the Orbitoides bed, the 

 marls contain numerous foraminifera, as seen at Folly's Point just east 

 of Port Antonio, and may indicate a deep water origin. 



Remnants of marls rich in Pteropod remains were found at two or 

 three localities upon the north-eastern coast of Jamaica up to an altitude 

 of 300 feet. The Pteropod marls indicate moderately deep water origin. 

 They are among the highly disturbed strata, apparently at or near 

 the base of the " White Limestone." They are unimportant in the 

 study of the recent topography. 



All the formations thus far referred to are greatly disturbed, and 

 there are several unconformities. The various deposits usually occur 

 in isolated tracts cropping out from beneath the overlying " White 

 Limestones " on account of the enormous denudation of the latter 

 series which even now covers five-eighths of the island. 



OLDER MIOCENE HISTORY — "THE WHITE LIMESTONES." 



This widespread series is white or light-coloured, impure Tertiary 

 limestone, with some arenaceous and marly beds. The structure varies 

 from thick massive beds to thin la5'ers, sometimes soft and marly, again 

 a fine-grained rock with an earthy appearance, in which some strata are 

 brecciated or flinty. Where not washed off by the tropical rains the 

 residual soil is a red earth similar to the residual products of Tertiary 

 limestones of Cuba, and other West Indian lands. Some of the beds 

 are very much honeycombed and caverns abound in them. This struc- 

 ture becomes so exaggerated on the highlands of the northwestern part 

 of the island, that a large area is rendered uninhabitable, owing to the 

 numerous sinks called "cockpits," two or three hundred feet or more 

 in diameter and deeper than they are wide. The remains of this 

 formation reach a thickness of more than 2,000 feet according to the 

 Jamaican geologists, and occur at altitudes up to 3,000 feet. It is this 

 series which forms the starting point of the present researches. 



These limestones cover the larger portion of the western t\vo-thirds 

 of the island, and form the coastal range of mountains which rises 

 abruptly from 1,000 to 2,000 feet above the sea. Indeed, it is probable 



