Mr. De la Beche on the Geology of Jamaica. 163 



On the Buff Bay River, and on the Southward of Charles Town, there are 

 thick beds of red sandstone and conglomerate, which pass, as before stated, 

 into the submedial rocks of that district ; these beds very much resemble those 

 at the head of the Hope River, and very probably belong to the same epoch 

 of formation. 



Among the Port Royal Mountains a considerable quantity of these rocks 

 will be observed, closely agreeing in composition with the red sandstones and 

 conglomerates of the Hope River, of which in fact they form the continua- 

 tion. 



Between Guava Ridge and the Yallahs River, but nearest the latter place, 

 there are thick beds of very compact siliceous sandstone, which apparently 

 belong to the red sandstone formation of Jamaica ; some parts of it are so 

 quartzose as to resemble M. von Humboldt's description of his "Roche de 

 Quartz Secondaire */' which he mentions as occurring in the Andes of Peru 

 between the 7th and 8th degrees of southern latitude. He states that this 

 rock is less developed on the eastern than on the western side of these moun- 

 tains, and that on the latter it is many thousand feet thick, and replaces the 

 gr^s rouge. 



Near Cocoa Walk estate on the Yallahs River, St. David's, twisted beds of 

 brown conglomerate, in which porphyry pebbles are abundant, are seen by 

 the road side on the right bank of the river ; these are much mixed with slate 

 clay, which is also twisted and contorted, and resembles that found among the 

 coal measures of the Hope River. These rocks are also observable on the 

 left bank beneath a mountain capped by the white limestone formation, and 

 the whole of the conglomerate and slaty beds are referrible to the rocks under 

 consideration. 



SuPERMEDIAL, OR SECONDARY RoCKS. 



Porphyrilic conglomerate associated with Porphyry and other Trap rocks. 

 — These rocks would, according to the views of those geologists who consider 

 red sandstone {grh rouge) as one great formation, in which coal measures 

 are subordinate, be classed with the red sandstones and conglomerates above 

 noticed. I have however here separated them, as they are, in Jamaica, asso- 

 ciated in a remarkable manner with porphyry and trap rocks, which the others 

 are not. 



The great characteristic of the conglomerate is, that the pebbles contained 

 in it are principally, and in some cases entirely, composed of various kinds of 



* Essai Geognostique sur le Gisement des Roches, p. 231, &c. 



