HILL: GROLOGY OF JAMAICA, 91 
often accompanied by shells of Mollusks, Echini, etc. In greatly altered 
reef rock the coral heads and marls become consolidated into firm semi- 
Crystalline white limestones, marked by irregularity of texture and 
humerous minute cavities representing the original interspaces of the 
Coral skeleton, or sometimes representing places from which the coral 
Structure has been dissolved away. ‘These cavities are frequently filled 
With red clay or sinter. 
This reef rock not only in Jamaica, but in Barbados, Cuba, Panama, 
Haiti, 3uadaloupe, and elsewhere, has an individuality whereby it can 
Usually be distinguished from white limestones of other than reef rock 
69 
7 
as AS: / 
Fiaurn 28. Showing Composition of Old Reef, 18 Mile Post, near Hopewell. 
Origin, Even when greatly altered by interstital change, true reef rock 
shows by the traces of reef coral structure and by its rough, cavernous, 
crystalline, and altogether unhomogenous texture its original nature, 
Hand specimens showing no coral structure can be selected from a mass 
of reef rock, for mud, coral débris, molluscan shells, and even shallow 
Water Foraminifera often fill considerable spaces between the coral heads. 
Such specimens are exceptional occurrences, however, and do not war- 
"Ant the frequent generalization that great masses of limestone, which 
Show no signs of coralline texture, may often be of coral reef origin. It 
May be considered reasonably certain that a rock mass in which remains 
9f reef corals are not visible is not coral reef rock.! 
IR 4 : fl : 
Coral reef rock is of very varying composition ; the coral grows in hummocks 
Separe A a 
“parated by more or less narrow spaces which are filled up by coral sand, broken 
d 
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