1897-98]- LATE FORMATIONS AND GREAT CHANGES OF LEVEL IN JAMAICA. 335 



fossils, only occurring further north, belong to temperate waters), the 

 exact epoch of change is not determinable. However, the succession of 

 physical breaks can be established beyond doubt, without impairing 

 the value of the determinations, even if the terrestrial movements 

 commenced a little earlier in one locality than in some other. In the 

 physical history of the West Indies, a wonderful degree of uniformity, 

 ■over vast regions, characterizes the later geological periods. 



As the upper Miocene fauna of the northern continent belonged to 

 temperate, in place of tropical forms of the earlier epoch, some great 

 physical cause must have produced the change, and thus we may 

 suggest that the elevation of the West Indies occurred before the 

 later Miocene period; consequently the great erosion of Jamaica 

 seems to date to an epoch before the Pliocene period. The physical 

 changes in the island were accompanied by great dynamical disturb- 

 ances, which not only elevated the land but also folded, distorted and 

 fractured the heavy bedded " White Limestones." While these de- 

 rangements of Miocene strata also occurred in Cuba and San Domingo, 

 the corresponding beds in Florida and Georgia are not dislocated or 

 upturned. 



Late Pliocene (?) beds rest upon the Miocene surfaces, which are 

 now often eroded below sea level. At that time the relative elevation of 

 the interior of the island, compared with the coastal regions, appears to 

 have been much less than at present. As there are marine accumula- 

 tions, referable to the late Pliocene epoch, preserved, it becomes possible 

 to form some idea of the different characteristics of erosion during the 

 Mio-PHocene elevation, and the degradation, subsequent to the accumu- 

 lation of the Layton beds, which are provisionally referred to the end of 

 the Pliocene period. 



In the highlands, the general denudation has reduced the old 

 Miocene surfaces so that the limestones form ridges or mountains, and 

 elevated base planes of erosion, largely completed during the Pliocene 

 elevation (as shown at m m Figure r, page 327). The degradation of 

 the island since the late Pliocene (?) deposits is characterized by the 

 formation of deep valleys, often broad (Fig. i, Plate II, opposite), and 

 dissecting the older base levels of erosion. The broad embayment- 

 like valleys, several miles wide (see Figure 3, page 336), among the 

 mountains upon the southern side of the island, are largely features of 

 the Pliocene denudation, more or less modified in later times. Of the 

 same character are the fewer coastal indentations on the northern side 

 of the island such as at Annatto Bay, Montego Bay, and Lucea Bay 



