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 
there were several centres of this eruption. The débris 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 Report. 
The next event in Jamaican history was the degradation of the 
Mucleal 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 
"T more, attests the existence of a high pre-existing land, and the 
Wundant 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 débris, and beds of the older igneous pebble reassorted, and 
the scarcity of animal remains, indicate rapid erosion and deposition. 
he uniform alternations, the wide extent of the formation, and the 
“casional presence of marine fossils, show that the material was sorted 
m 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 doposits, and the widespread occurrence of similar 
formations in the West Indies, suggests the existence in the region 
Mt that time of larger land arcas than the mere nucleal summits we 
‘Wve described. 
There is also evidence that subsidence accompanied this deposition, 
"nd 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 
‘tervals until the close of Miocene time throughout the Antillean 
egion, 
Tho 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 
completely overthrown, as shown in the illustration on Plate XXII. 
19 epoch of this folding could be easily assigned to a later disturb- 
“tee, such as that at the close of the Miocene, were it not for the fact 
iat nono of the overlying and succeeding strata exhibit such intensity 
y disturbance. The latter occur in gentler and more open folds. 
€——— 
nn 
ne DES 
Eu EEE 
== 
