hill: geology of JAMAICA. 49 



a^ain, as in the canyon of Plantain Garden River in Portland, where the 

 Cretaceous rocks of Jamaica were first noted by Barrett,^ a single 

 stratum of limestone is interbedded between overlying and underlying 

 tuffs, conglomerates, and clays. Sawkins noted in southwest Portland 

 *' thin beds of Cretaceous limestone, interstratified with thick porphy- 

 ritic breccias and conglomerates, enclosing contemporaneous trap rocks." ^ 



The writer tried to visit all the localities mentioned, three of which, 

 Clarendon, Jerusalem Mountain, Westmoreland Parish, and Bath, in 

 St. Thomas, may be taken as typical. These are in the central, western, 

 and eastern portion of the island respectively.^ 



Jerusalem Mountain Section. — In at least one locality Cretaceous 

 limestones occur in extensive beds. This is near the extreme west end 

 of the island at Jerusalem Mountain in the parish of Westmoreland. 

 This was probably sufficiently remote from the centres of igneous activ- 

 ity to permit undisturbed oceanic conditions and continuous growth of 

 life. Jerusalem Mountain is a low, isolated hill standing 570 feet above 

 the sea and about 500 feet above the surrounding valley plains. It is 

 composed entirely of Cretaceous limestones and dull yellow clays, except 

 at its eastern base, where the Tertiary limestones rest unconformably 

 against it, probably by faulting. The rocks dip slightly to the east. 

 Here we made the following section : — 



Later Formations at Foot of the Hill. 



IV. Yellow shale resembling Richmond beds, with beds of lime- Feet, 

 stone ; weathers into purple colors 25 



III. Minho Beds. Purple clays and blotched shales dipping east 60 



11. " White limestone " in bluish shale, fossils Tertiary ] ... 50 



I. Level of valley plain of Mount Eagle. Alluvium .... 60 



Section of the Hill. 

 VI. 14. Summit of brown marls with Alectryonate oyster in 

 thin limestone slabs, Pholadomya, etc 25 



V. 13. Yellowish limestone with small fossils 15 



12. Red purple clay 10 



II. Dimension layers one foot thick, of impure limestone with 

 A-lectryonate oyster 10 



10. Yellow marl 22 



9. White fossiliferous limestone, Caprinella 20 



1 Quart. Jour. Geol. Soc. London, Vol. XVI. pp. 324-326. 



2 Jamaican Reports, p. 74. 



VOL. XXXIV. 4 



