52 bulletin: museum of comparative zoology. 



From the data presented, with the exception of the Jerusalem section, 

 and the observations of otlier writers, it is evident that the limestones 

 and marls containing the Cretaceous faunas occur interbedded wdth the 

 conglomerates, tuffs, and shales of the lower portion of the Blue Moun- 

 tain Series, and become less and less conspicuous in ascending sequence. 



Sawkins ^ has spoken of the limestones as " being disposed in a zone 

 around the higher elevations/' and as " forming a zone around the great 

 nucleus of upheaval of the island." ^ If tliis were correct, it might be 

 possible that much of the Blue Mountain Series is antecedent to these 

 beds. This statement is not accurate, however, for these limestones are 

 found not only around but folded m the plexus of beds constituting the 

 highest mountains, occurring on Blue Mountain Peak as high as Abbey- 

 Green, 4,200 feet above the sea. Even if true, the statement would be 

 applicable only to the eastern end of the island, for all exposures of 

 these beds west of the longitude of Spanish Town (except Jerusalem) 

 are in the central basins where erosion has cut down to them through 

 the overlying White Limestones and Blue Mountain Series. This is 

 especially so at Clarendon, where the beds are covered by hundreds of 

 feet of the same rocks which constitute the high summits of the east. 



The tuffs, igneous pebble, and boulders of the lower subdivision are 

 composed almost entirely of hornblendic material, — andesites and por- 

 phyries, — which shows that this was the chief eruptive material of 

 Jamaica during this epoch, and of which the Minho beds apparently 

 represent the debris of the last expiring extrusion. These indurated 

 tuffs often have a superficial resemblance to altered clays and sandstones, 

 and this aspect, in addition to undoubted occasional igneous metamor- 

 phism, was the reason why the beds were m places called the "Metamor- 

 phosed Series." 



All beds of the lower subdivision, taken collectively, represent the 

 product of disturbed conditions, such as active vulcanism accompanied 

 by the piling up and contemporaneous degradation of vast quantities of 

 igneous material much of w^iich was deposited below sea level, alternat- 

 ing with short periods of quiescence, when shales and marls were per- 

 mitted to accumulate and sparse faunas to gain temporary foothold. 

 The alternations of shale and igneous material in the Blue Mountain 

 Scries indicate alternating conditions of sedimental placidity and vol- 

 canic extrusion, and a conflict between disturbed and quiescent condi- 

 tions of deposition w^hich finally culminated in the establishment of the 

 latter in the succeeding Richmond epoch. 



1 Jamaican Reports, p. 105. 2 Ibid., p. 22. 



