\ 



hill: geology of Jamaica. 45 



or "made up of conglomerates " as he states in another pLace.^ Duncan 

 and Wall,* whose opinions were based on the field observations of Wall, 

 state that " It is difficult or impossible to determine the relation of the 

 conglomerate and Cretaceous groups. This is especially the case in the 

 highly mountainous eastern parts of Jamaica, where traces of almost 

 obliterated Ilippurites [lludistes] and other fossils are detected in 

 strata which from their confined position could not otherwise be classi- 

 fied stratigraphically." They state that in Clarendon, however, " the 

 lowest members of the Cretaceous Series frequently consist of a thin 

 bed of conglomerate formed of the harder material of the porphyries." 



Barrett said* that it is " evident that the igneous rocks forming the 

 base of this series, and interstratified with some of the shales and con- 

 glomerates, were erupted prior to the deposition of the Cretaceous 

 limestone, and at intervals of time sufficient for the formation of aqueous 

 interbedded strata." 



The writer in his own investigations and in the literature of the 

 island has found no proofs that the base of the section is limestone. 

 The limestones of the Bath and Clarendon sections are clearly inter- 

 calations in vast beds of igneous debris. The limestones are certainly 

 the oldest rocks paleontologically identifiable, but from the data to be 

 given the writer believes the fossiliferous Cretaceous beds are local 

 occurrences in the great and tangled series of tuffs and conglomerates, 

 the latter of which constitute the visible base of the section. These 

 are detrital formations of volcanic debris of unknown origin. The 

 writer searched the exposures with particular care, but in vain, for evi- 

 dence of some older or lower lying rocks beneath the classic formations 

 of the Blue Moimtain Series such as are reported in Cuba and Haiti, 

 or a trace of ancient massifs or volcanic vents from which the detrital 

 igneous rocks were derived. 



The Clarendon Section. — The best partial section of the lower division 

 of the series is in the parish of Clarendon, along the St. Thomas and 

 Minho Rivers, where all the beds, not including the lowest and highest 

 of the series, are exposed in a less disturbed condition than elsewhere. 

 This parish was considered by Sawkins * and Wall and Duncan ^ to 

 afford the most complete exposition of the relationship of the older 



^ Jamaican Reports, p. 307. 



2 Quart. Jour. Geol. Soc. London, 18G5, Vol. XXI. p. 3. 



8 Quart. Jour. Geol. Soc. London, 1860, Vol. XVI. pp. 32i-326. 



* Jamaican Reports, p. 25. 



* Quart. Jour. Geol. Soc. London, Vol. XXI. p. 4. 



