422 Dr. C. T. Trechmann— 



T 



The Gretaceous and Tertiary Question in Jamaica. 



By C. T. Trechmann, D.Sc, F.G.S. 



HE geology of Jamaica compared with that of some areas of the 

 earth's crust is neither very involved nor very difficult of 

 interpretation. Considering the "length of time that has elapsed 

 since it was first studied and the easy accessibility of many parts 

 of the island, it should be fairly well known and should form a 

 key for the interpretation of the structure of the larger and less 

 well-known islands of Haiti and Cuba, and also of Porto Eico and 

 the smaller islands forming the group of the Greater Antilles. 



Unfortunately, confusion has arisen on more than one occasion 

 concerning the correct attribution of one or other of the sedimentary 

 formations of the island. I desire briefly in the present paper to 

 call attentipn to some of the errors that have arisen and, as I hope, 

 to correct what I consider to be the latest and one of the most 

 serious of these errors, namely that referring to the reputed com- 

 mingling of Cretaceous and Tertiary faunas in certain of the beds. 



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Fig. 1. — Locality Sketch-map of Jamaica. 

 Roughly speaking, the island of Jamaica may be said to be made 

 up of three great constructive units; beginning with the lowest, 

 these are : — 



1. The Blue Mountain series, consisting of more or less highly 

 folded and locally more or less metamorphosed and intruded series 

 of fragmental and calcareous sedim,entary deposits of Cretaceous 

 and early Tertiary age. 



2. The covering mass of Tertiary limestones, comprising the 

 Yellow Limestone overlain by and generally merging up into the 

 great White or Cockpit^ Limestone. 



3. The locally developed marginal deposits, comprising the 

 gravel beds and white foraminiferal marls, and the beds con- 

 taining the well-known Bowden fossils, together with various Post- 

 Pliocene accumulations. 



^ Cockpit Country is the name given to an area in the north-western central 

 part of Jamaica, but sinks of more or less cockpit-like shape are developed 

 wherever the White Limestone forms plateaux or elevated tracts. 



