100 bulletin: museum of comparative zoology. 



themselves, such as that at Barbican, which can be seen to be clearly- 

 deposited upon a surface horizontally eroded across the vertical structure 

 of the old Blue Mountain Series. Similar submerged plains are now 

 occupied by the growing reefs around the island. That these elevated 

 reefs were formed on former land surfaces which had been submerged 

 and were in the process of emerging, is attested by every topographic 

 feature. The streams have cut continuously downward through steadily 

 risinf^ old reefs, leaving no evidence of alternating periods of drowning 

 between them, such as veneerings of later sea deposits across them. 



Our studies of the Oceanic Series have shown that true reef building 

 corals do not occur in the great mass of white limestone composing the 

 structure of the back coast country of Jamaica, or at altitudes greater 

 than 70 feet. Our paleontologic discussion also shows that the true 

 modern reef building coral species first appear doubtfully in the Bowden 

 beds, then sparingly in the Manchioneal formation, along the coast be- 

 tween Mulatto Bay and Manchioneal and near Round Point, Hanover. 

 These and all succeeding beds containing reef coral occur only imme- 

 diately adjacent to the present seacoast and unconformably against the 

 pre-eroded perimeter of the main area of the island. 



These reefs are laid down on various formations from the Richmond 

 shale to the Manchioneal beds, respectively. On the north coast of 

 the island they are seen in contact with the Richmond, ^Montpelier, 

 Moneague, and Manchioneal formations, while upon the south side 

 they lie upon the Cobre, Bowden, and Montpelier. 



In general, the old reef rock of Jamaica consists of three distinct for- 

 mations occurring at three levels, 70, 25, and 10 feet (or less) respect- 

 ively. From the persistency of these three levels on the north, east, 

 and southwest end of the island, it is evident that their present position 

 above the water is due to continuous epeirogenic elevation after the 

 present outlines of the island had been chiefly defined. 



Miscellaneous Coastal Formations contemporaneous in Origin 

 WITH the Elevated Reefs. 



The present land margin is not continuously fringed by growing 

 reefs, but they occur in interrupted patches, alternating here and there 

 witli strips of different kinds of bottom, such as alluvial deposits op- 

 posite the mouths of rivers, shell sand, or lagoon mud. Similar con- 

 ditions prevailed during the time of the creation of the old reefs, and 

 houce wc find with theni many diverse formations of contemporaneous 

 origin, some of which will now be described. 



