hill: geology of Jamaica. 105 



In addition to the true islets there is a circular head projecting from 

 the land as a peninsula, the narrow neck of which, if severed, would 

 leave an islet of the kind we have described. This and the land im- 

 mediately back of the island is a mangrove covered morass of the type 

 we have just described as the Montego formation. 



Nowhere can so grand a combination of erosive and constructional 

 processes or the successive formations of the Coastal Series, as a wiiole, 

 i)i^.d their relations to the older formations of the island, be seen in a 

 single view as at Montego Bay. This is a great indentation into the 

 coast, the back country of which is composed of beautiful hills covered 

 with tropical upland vegetation, rising in a series of grand terraces to 

 a height of 1,000 feet or more, as shown in Figure 6 and on Plate XX. 

 This plain is composed of the following formations of the Coastal 

 Series : the Manchioneal beds, the twenty-five foot level or middle old 

 reef, the low level Soboruco, and the Montego formation, while the 

 Bogue Island formation barely appears above the waters of the bay. 

 In the shallow bay fringing reefs are growing, and Mollusks, Echinoderms, 

 and other sea shells are dying and contributing shell debris, which near 

 the shore is mingling with the aggradational alluvium brought down 

 by the rivers. Elsewhere it forms great deposits of purest calcareous 

 sand. 



The Montpelier formation, with its contorted beds of chalk and flints, 

 forms the back coast hills in which this scene is set, and against which 

 the various other formations lie in unconformable contact. Fragments 

 of the yellow marls allied to the Manchioneal formation can be seen 

 against this on the west point of the harbor between the mouth of 

 Great Eiver and Round Hill Point. The old Soboruco, now converted 

 into a white limestone rising fifty feet or more, constitutes the opposino- 

 northeast point of the bay. The railway station back of the town is 

 upon a low level plain made up of shell bearing marls equivalent to the 

 Falmouth formation, while the low coast Soboruco borders the sea at 

 the city and Round Hill Point. The Montego formation occupies a still 

 lower plain, almost or at sea level, cut out of the low Soboruco and 

 Falmouth formation, as seen in the morasses south of the city. The 

 indentation comprising the bay and coastal plain was cut by the com- 

 bined forces of erosion baselevelling the land, and wave action indent- 

 ing the shore, probably in late Pliocene time ; afterwards this plain was 

 submerged, veneered by deposited sediment from the land, and inhabited 

 by growing reefs. Later elevation brought the interior margin of the 

 bay above the water, constituting the present low land extending be- 



