Mf. De la Beche on the Geologi/ of Jamaica. 183 



llie lower part of which Kingston is situated. This plain presents an inclined 

 surface, falling- gradually from a height of about 700 feet, which it attains 

 where it abuts against the mountains that bound it on the north. It is almost 

 wholly composed of diluvial gravel, consisting principally of the detritus of the 

 St, Andrew's and Port Royal mountains, and evidently produced by causes not 

 now in action, but derived from those mountains in the same manner and pro- 

 bably at the same period with the numerous tracts of European gravel which 

 have resulted from the partial destruction of European rocks. The moun- 

 tains which bound this plain are composed of white limestone, porphyry, 

 syenite, greenstone, red porphyritic conglomerate, and siliceous sandstones, 

 with red sandstones and conglomerates of an older date. Rounded pieces of 

 all these rocks, those of the first being, however, very rare, form the diluvial 

 gravel of Liguanea, which has resulted from their partial destruction. Thoug-h 

 the pebbles are not in general of great size, there are some large blocks of 

 siliceous sandstone among them near the Hope estate, and I have seen boul- 

 ders of greenstone near the base of the Long Mountain. 



The Hope River, with the Mammee River which falls into it, drains a con- 

 siderable portion of the St. Andrew's Mountains, and loses itself, when the 

 waters are low, among the Liguanea gravels, where the latter meet the solid 

 strata of the mountains ; but when swollen by heavy tropical rains, the river 

 rushes with considerable force through the defile near the Hope Tavern, and 

 traverses the gravel plain, which it has cut to a considerable depth : so that 

 in fact the causes now in action tend to destroy the diluvial gravel plain of 

 Liguanea rather than add to it. The section of these gravels, which the 

 river has formed by cutting its bed, cannot be less than from 200 to 300 feet 

 in depth near the Hope Tavern *. 



Proceeding up the Hope Valley, a part of the road displays a portion of di- 

 luvium (the rounded pieces of rock in which are large) resting upon a pro- 

 jecting portion or shoulder of the mountain, which rises high above the river. 



In addition to the Hope River, numerous gullies formed by heavy tropical 

 rains cut the diluvial plain of Liguanea in various directions, so that every 

 stream that traverses it, tends to destroy it. 



This plain descending gradually into the sea, and being in a great measure 

 defended from the ravages of the latter by the Palisades (a sand-bank that 

 extends several miles, and joins the town of Port Royal with the main land), 

 alluvial matter is deposited in some parts of the shore, more particularly 



* The Tavern itself is 698 feet above the level of the sea according to my barometrical obser. 

 vations, and the diluvial gravel rises above it. 



VOL. II. — SECOND SERIES. 2 B 



