718 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



of the island, it is difficult to infer the situation of the near-by land from which the material 

 was derived; some of it may have come from the old nucleus of Blue Mountain Ridge, but in 

 our opinion this was not of sufhcient size to afford all the material. These facts, together 

 with the presence of foreign material, are at least strongly suggestive of the occurrence of land 

 areas during this epoch, concerning the locality of which present knowledge is wholly wanting. 



The Cambridge formation is named after the typical locality of its occurrence at Cambridge, 

 between Ipswich andJVlontpelier, in the parish of St. James, in the northwestern portion of the 

 island, near the junction of the boundaries of St. James, Hanover, and Westmoreland. 



In places the Richmond beds grade up into irregular alternations of impure clay, marls, 

 and yellow limestones, which, in general, occupy a transitional position between the obviously 

 land-derived beds of the Blue Mountain series and the ocean-derived limestones of the Oceanic 

 series. Argillaceous calcareous marls appear in the upper part of the Richmond beds, become 

 successively more and more frequent, and finally dominate. These are accompanied by thin 

 beds of impure blue limestone of a segregational character, oxidizing yeUow on weathering and 

 alternating with the naarls which gradually increase in thickness and relative proportion until 

 they preponderate. Finally these yeUow limestones become more purely calcareous in ascending 

 series as the sediments become clearer and freer from land-derived raaterial, until they finally 

 pass into the purer White limestones. 



As he was not able to correlate certain divisions of the Cambridge formation 

 precisely with one another, Hill distinguished them under the names of Catadupa 

 and Chapelton beds. After describing these different occurrences, he continues : ^^^ 



There are several paleontologic and stratigraphic features of the Cambridge beds which 

 are' peculiar and will require more extensive field work for final explanation. We have reason 

 to believe that the beds are not connected but occur in broken patches, which, at least in their 

 lower portion, like the Cretaceous beds, represent sporadic colonies of lime-making organisms, 

 which found temporary foothold at intervals during a period of turbulent deposition generally 

 unfavorable to a large development of marginal life. These deductions are based upon the fact 

 that in no two localities are the sequence of sediments or association of species identical, while 

 in others the beds do not appear between the Richmond and the Montpelier. Furthermore, the 

 fossiliferous horizons of the Lower Cambridge are so like some of the Cretaceous that the one 

 has been frequently mistaken for the other. The mixture of Cretaceous Rudistes and Eocene 

 corals and Mollusca at Catadupa, as seen by us, and of Orbitoides and Rudistes in Portland, as 

 noted by Barrett, indicates a transgression of Cretaceous life into the Eocene and further 

 denotes the anomalous nature of this formation. 



These beds, while showing sedimentary relations to the Richmond, undoubtedly represent 

 a transitional step in the deepening which later produced the Montpelier formation. In some 

 places it seems perfectly conformable beneath the latter, while again, as shown by Brown 

 and seen in several places by us, they are unconformable. These apparently irreconcilable con- 

 ditions can probably be explained upon the hypothesis that the island was undergoing subsidence 

 during the Cambridge epoch, although parts of it were then dry land, which was still further 

 covered by the Montpelier beds during the succeeding epoch. As shown in another chapter, 

 the age of these beds, although containing a remarkable mixture of Cretaceous and Tertiary 

 fossils, is undoubtedly Eocene, and \yiih the Richmond beds they constitute the Eocene system 

 in Jamaica. 



Of the White limestones, Hill distinguished two series, the Oceanic and Coast 

 series. He says:**'*'^ 



The transitional Cambridge beds grade up into rocks of organic oceanic origin. These are 

 the White limestone formation of the official Jamaican reports. The}'' have no genetic rela- 

 tionship with the rocks of the Blue Mountain series and difl'er from them in every physical and. 

 chemical aspect. 



