1826.1 Geological Society. 231 



pompact, and then strongly resembling the compact varieties of 

 Jura limestone. The strata are usually very thick, varying from 

 three to twenty feet in breadth. In some districts this rock is 

 interstratified with thick beds of red marie and sandstone, and 

 white chalky raarles. The compact limestone constitutes the 

 middle part of the formation. The lower beds consist chiefly of 

 sands and marles, sometimes associated with bluish gray compact 

 limestones, at others with beds of earthy yellowish white lime- 

 Stone, containing an abundance of organic remains, viz. Echinites, 

 OstrecR, and particularly large species of Ceritliium. The upper 

 beds of the formation are rather chalky, sandy, and marly, and 

 contain numerous remains of the genera Comus, Ceritliium, 

 Astarte, Natica, &c. and near the sea-coast a great quantity of 

 Corals, which, frequently, have almost a recent appearance. 



Above the white limestone formation, beds of conglomerate 

 and sandstone are visible on many points, particularly on the 

 edges of the Savannahs ; whence the author calls them the 

 Savannah sandstones. 



The upper beds of all visible in the island consist of diluvium 

 and alluvium. The former shows itself on a very large scale, 

 covering the surface of the principal plains, particularly that of 

 Liguanea. 



It consists of rounded fragments of the rocks which compose 

 the neighbouring mountains. The Hope river, which has cut its 

 channel through the plain of Liguanea, has exposed sections of 

 these diluvial gravel-beds, from 200 to 300 feet in thickness. 

 The greater part of the large plain of Vera and Clarendon is also 

 composed of diluvium. The pebbles of these beds consist 

 chiefly of trap rocks ; those of white limestone are compara- 

 tively rare, this rock appearing to have failed in resistance to 

 the force of attrition by which its fragments were attacked. The 

 separation between the diluvium and alluvium is not very decided; 

 but deposits of the latter class have certainly been produced in 

 considerable quantities along the course of many of the rivers, 

 and on parts of the shore, particularly between Kingston and 

 Port Henderson, in front of which extends a long sand-bank, 

 called the Palisades. 



Mr. De la Beche's paper concludes with an interesting com- 

 parison of the Jamaica formations with those of Mexico and 

 South America, as described by M. de Humboldt. The gray- 

 wacke of Jamaica would seem to be continued in Mexico, with 

 its accompanying trap rocks, and dark-coloured limestones. In 

 South America it is absent, and its place is supplied solely by . 

 porphyries, syenites, and greenstones, which are developed there 

 on a very large scale. The red sandstone which is found in 

 Jamaica, occurs very extensively in the neighbouring parts of 

 the itmerican continent. A formation analogous to the white 



