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bulletin: museum of comparative zoology. 



Generally the Soboruco or old reef rock occurs immediately at the 

 water line, forming an abrupt undermining bluff from five to ten feet 

 hic'h (See Plate XXVIII). In addition to the low level formation, two 

 distinctly higher reefs are sometimes discernible, often a hundred yards 

 or more back of the present beach line, at altitudes of 25 and 70 feet 

 respectively, and constituting distinct formations. Owing to the fact 





< SEA LEVEL 



Figure 29. Relations of Elevated Reefs near Hopewell. 



that the old reefs of these three levels are conspicuous bench marks 

 whereby the succession of other formations can be determined, we shall 

 discuss them, where separable, under the names of the Coast Soboruco, 

 Barbican, and Hopewell formations, respectively. Where not separable, 

 or where their exact equivalence is indeterminate, the general term 

 Soboruco will be used. Furthermore, while we believe the sequence of 

 all the formations of the Coast Series is as given in the general table, 

 page 42, for the purpose of discussing the reef made formations together, 

 tliat order will be temporarily departed from and tiie latter will now be 

 described. 



The best exposures ^ of the Soboruco observed by us were along the 

 road following the coast of the east end of the north side of the island 

 between Port Antonio and Northeast Point, but the sequence of the suc- 



shells, Foraminifera, etc. Microscopic examinations of fragments of limestone 

 broken from coral reefs sometimes show no traces of coral structure. Coral, more- 

 over, is more readily decomposed than shell, sand, or foraminiferal limestones." — 

 Nat. Sci., November, 1897, p. 290. 



" Coral-reef Rock. — The rock forming the coral platform and other parts of the 

 solid reef is a white limestone, made out of corals and shells. In some parts it 

 contains embedded corals; in others, it is as compact as any Silurian limestone and 

 without ft fossil of any kind, unless an occasional shell. The compact non-fossil- 

 iferous kinds are formed in the lagoons or sheltered channels; tlie kinds made of 

 broken corals, on the seashore side, in the face of the waves ; those made of corals 

 standing as they grew, in sheltered waters, where the sea has free access. Large 

 portions nrc a coral and shell conglomerate." — ^Linual of Geology, by James D. 

 Dana, Fourth Edition, New Haven, Conn., 1895, p. 14G. 



1 TIjg distribution of the Soboruco in Jamaica is well shown on the Geological 

 Map accomjKUiying tiie Jamaican Reports, and in tlie text it is discussed under the 

 licad of the Toast Limestone. The text of the Reports gives only passing atten- 

 tion to these rocks, and does not differentiate them into distinct formations. 



