HILL: GEOLOGY OF JAMAICA. 157 



period. Furthermore, the species themselves, their faunal assemblage, 

 and the circular arrangement of the colonies around the nuclei of 

 the Blue Mountain and Clarendon ridges may possibly indicate that 

 tiiere were several centres of this eruption. The debris of this event 

 was enormous. The thickness of that portion which now survives can 

 be assumed to be at least five thousand feet. The former extent and 

 relations of these late Cretaceous volcanic outbreaks in the Antilles is 

 now concealed by the coatings of later formations, but they were not 

 peculiar to Jamaica alone, as shown later in this Keport. 



The next event in Jamaican history was the degradation of the 

 nucleal volcanic heaps by erosion, — a fact recorded in the sediments 

 of the upper part of the Blue Mountain Series, especially the Rich- 

 mond beds. The thickness of these sediments, aggregating 1,500 feet 

 or more, attests the existence of a high pre-existing land, and the 

 abundant plant remains they contain show that it was thickly covered 

 with vegetation. The nature of the sediments themselves, which are 

 of impure land-derived material, carbonaceous clays, sandstones of 

 volcanic debris, and beds of the older igneous pebble reasserted, and 

 the scarcity of animal remains, indicate rapid erosion and deposition. 

 The uniform alternations, the wide extent of the formation, and the 

 occasional presence of marine fossils, show that the material was sorted 

 in shallow waters. This fact, together with the presence of a few 

 pebbles of foreign origin, the absence so far as known of any distinct 

 delta or estuarine deposits, and the widespread occurrence of similar 

 formations in the West Indies, suggests the existence in the region 

 at that time of larger land areas than the mere nucleal summits we 

 have described. 



There is also evidence that subsidence accompanied this deposition, 

 and that the two events were so compensatory that the depth of 

 bottom did not materially change. These events were also closely 

 followed by folding of the strata, — a process which was repeated at 

 intervals until the close of Miocene time throughout the Antillean 

 region. 



The strata of the Richmond beds are not only everywhere folded, but 

 near Lucea, in the western end of the island, they are closely flexed, and 

 are completely overthrown, as shown in the illustration on Plate XXII. 

 The epoch of this folding could be easily assigned to a later disturb- 

 ance, such as that at the close of the Miocene, were it not for the fact 

 that none of the overlying and succeeding strata exhibit such intensity 

 of disturbance. The latter occur in gentler and more open folds. 



