hill: geology of JAMAICA. 115 



PART III. 

 Paleontology of the Jamaican Sequence. 



The entire Jamaican section contains many unfossiliferous horizons. 

 In other words, while there are a few zones^ where abundant macro- 

 scopic fossils occur in abundance, a large part of the 10,000 feet of strata 

 are non-fossiliferous. The lower Blue Mountain Series are mostly with- 

 out fossils because of the disturbed conditions during their deposition. 

 The upper portion of the Series is likewise mostly barren, owing to the 

 turbulence of the muddy waters in which it was laid down. The deep 

 water Tertiary white limestones, although largely composed of micro- 

 copic organisms, contain vast thicknesses of rock with no macroscopic 

 organic remains. This is due to the fact that these limestones were 

 deposited at great depths, where fossil making forms other than Radio- 

 laria were few in number, and the calcareous skeletons of such as did 

 exist were dissolved by deep sea waters. 



On the other hand, the many changes of the character of the habitat, 

 such as the introduction into the sea of the material of the Cretaceous 

 volcanic outbreaks and changes of level in the later epochs, have inter- 

 rupted the continuous existence of such littoral faunas as leave the most 

 abundant remains and which from time to time may have secured foot- 

 hold around the island prior to late Oligocene time. Thus it is that 

 the few colonies of Upper Cretaceous life which obtained ephemeral 

 existence around the margins of the island were deficient in species ; 

 the Cambridge forms, a little more diversified, and the Bowden and 

 later species are numerous, as the surrounding seas afforded more con- 

 stant and favorable conditions for the life of organisms. 



The paleontology of Jamaica is difficult to discuss, because many pre- 

 viously known species have been described from miscellaneous collections 

 (made by others than the describers) by naturalists who had not visited 

 the island and had no conception of the stratigraphic sequence, position, 

 association, or exact locality of the forms. Such studies are valuable 

 so far as they result in the correct naming of species, but they a^e too 

 often accompanied by an unfortunate duplication of names and conflict- 

 ing generalizations and deductions. Thus one author referred all the 

 invertebrate faunas of the whole Tertiary and later formations, without a 



^ These horizons are marked with an asterisk in the columnar section on page 42. 



