EARLIER TERTIARY (EOCENE AND OLIGOCENE). 719 



The interpretation of the white limestones has been one of tlie greatest problems of Jamaican 

 geology. There have been so many diverse opinions concerning their age and sequence that 

 it is almost impossible to obtain from current literature any approximation of their true rela- 

 tions and significance. The difficulties can be readily seen by any one who reads the conflicting 

 and apparently involved conclusions in the Jamaican reports. The fragmentary descriptions 

 of their local occurrence are frequently well written, but through lack of correlation and erroneous 

 deduction they fail to clear up the sequence and age of the beds. * * * 



The truth is, the white limestones of the Jamaican sequence represent several distinct 

 formations and ages, from Vicksburg to recent inclusive, but that the greater portion of it, as 

 I shall show, is of old Oligocene age. There are even some white limestones in the Cretaceous 

 in Clarendon which are almost lithologicaUy indistinguishable from those of the Tertiary. In 

 recent years English geologists have observed the discrepancies of previous interpretations of 

 the white limestone and suggested, from specimens of the material sent them, that at least an 

 upper and lower division might be distinguished. Our investigations will show that not two 

 but several subdivisions can be made, and that the rocks hitherto classified under this general 

 head really belong to several distinct formations of two great series, the Oceanic and the Coastal, 

 the former constituting most of the rocks of this character and occupying large areas of the 

 interior upland, while the latter are confined to a narrow belt along the coast. 



The older white limestone formations, constituting the greater mass of these rocks, are 

 found in the upland area of the island and are all of Tertiary age. More exactly speaking, they 

 are of the Vicksburg stage, which is placed in the Eocene by some writers and in the Oligocene 

 by others. The later white limestone formations — including the Coast limestone of the Jamaican 

 reports, which we shall describe as the Falmouth formation, and the Hospital Point limestone 

 of Montego Bay — are of Pliocene, Pleistocene, and recent age. 



There has also been much vagueness concerning the origin of these rocks, accompanied by 

 an opinion on the part of many that they are of coral-reef origin. * * * 



Not the least important result of our researches will be a demonstration that the larger 

 thicknesses of these limestones are neither of molluscan, coralline, or reef-rock origin, but are 

 foraminiferal oceanic deposits and other offshore calcareous oceanic muds composed of organic 

 detritus laid down at depths below that at which reef rocks were formed and in periods of eo- 

 logic time prior to the appearance of the modern reef-building species in the sequence. * * * 



The upland white limestones or Oceanic series, as we shall call the Tertiary formations 

 under discussion to distinguish them from, the later deposits of the Coastal series, consist of 

 white limestones of varying texture and hardness, and probably aggregate 2,000 feet in thick- 

 ness. These present a perplexing series of surface and interstitial changes under the influences 

 of solution and oxidation, as explained in their detailed descriptions, which render their study 

 a difficult task. They consist of deeper-water organic deposits and are free from coral-reef rock, 

 littoral shell agglomerates (such as coquina, cantera, and caleche), beach wash, eolian debris, 

 or other clastic formations which characterize the rocks of the Coastal series. They contain few 

 macroscopic fossils by which their age can be independently determined, but this is fixed by their 

 microscopic fossils and their position between including fossiliferous horizons — the underlying 

 Cambridge beds and the overlying Bowden gravels and marls. 



In general, the Oceanic series occupies most of the plateau region, which practically includes 

 all the island under 3,000 feet in altitude outside of the Blue Mountain district, except its imme- 

 diate coastal borders. In the mountainous region of eastern Jamaica these rocks occur as a 

 high piedmontal peripheral border around that end of the island. In the western half of the 

 island the beds of the Oceanic series completely cover the old Blue Mountain series and occupy 

 the higher summits of that portion of the island. 



Owing to the elevation of the plateau region which took place after the deposition of these 

 beds, and the subsequent contraction of its oceanic borders by erosion and subsidence, the 

 coastward extension of the rocks is truncated and partially embedded near the littoral by the 

 still later formations of the Coastal series, which are deposited unconformably against them. 



