I860.] 



BARB.ETT JAMAICA. 



325 



'A 





Cr 



A quarter of a mile higher up the river there is a section of sonic 

 , . vertical beds of hmestone, probably older than the 

 & : o series already described. A bed of conglomerate sepa- 

 ■*■£ rates them from great masses of porphyry. This 

 £, section (see woodcut) exhibits thin bands of lime- 

 ■& stone, alternating with shale, containing limestone- 

 „5 nodules. Some of the thin bands of limestone are 

 crowded with fossils, principally Inoceramus, Hijp- 

 -5,1 purites, and a species of Bulla (?). 

 £ I These fossiliferous beds are succeeded by a bed of 

 conglomerate, 12 yards thick, composed entirely of 

 pebbles of porphyry, identical in structure and colour 

 with the adjacent mass. The conglomerate is not 

 altered at its junction with the igneous rock. The 

 porphyry in contact with the conglomerate is of a 

 purple colour, and contains small crystals of felspar ; 

 in some places it is made up of large felspar-crystals 

 £ imbedded in a dark cellular base (the cavities being 

 g. sometimes filled with kernels of carbonate of lime) ; 

 <£ and at the distance of an eighth of a mile it passes 

 into an amygdaloid. The porphyries are divided by 

 a bed of conglomerate 30 yards wide. 



A thick bed of grey limestone crosses the medial 

 ridge of mountains, at an elevation of 2500 feet above 

 the sea ; and at a distance of twelve miles from the 

 east coast its strike is N.W. — S.E., and its general 

 dip X.E. ; it rests on numerous alternations of igneous 

 rock, shale, and conglomerate. The following is the 

 descending order at Cold Kidge : — 



Grey limestone containing Hippurites, and with 

 black flints enclosing Ventriculites, Arc, resting on 

 a ragged surface of porphyry (the cavities in the 

 upper surface of the porphyry sometimes filled with 

 fossil shells). The porphyry is succeeded by a 

 thin bed of shale ; the shale by thick beds of horn- 

 blende-rock, divided by a bed of conglomerate en- 

 tirely composed of rolled fragments of the same ig- 

 neous rock. 



The porphyries and hornblende-rocks of these lo- 

 cality's are evidently interbedded, as they have not 

 altered the Btratined rocks in contacl with them, and 

 an- divided by beds of shale and conglomerate (the 



conglomerate being Composed of fragments of the 

 lower volcanic rock). 



There can he no doubt that the fossiliferous lime- 



stones, are of Cretaceous age, — the family Radiates 

 being characteristic of the Cretaceous rocks both oi 

 Europe and America, and Tnoceramus and Nerincea 

 being peculiar to Ifesozoic strata. 

 Sir H. De-la-Beche, in his memoir on tin- G< ologi 



i m 



O V 



SPJS 



c g 



