5 
2 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY, 
From the data presented, with the exception of the Jerusalem section, 
and the observations of other writers, it is evident that the limestones 
and marls containing the Cretaceous faunas occur interbedded with 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 this 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 in 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 hornblendie 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 débris 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 in 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 which 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 | 
Series indicate alternating conditions of sedimental placidity and vor 
canic extrusion, and a conflict between disturbed and quiescent condi- 
tions of deposition which finally culminated in the establishment of the 
latter in the succeeding Richmond epoch. 
1 Jamaican Reports, p. 105. 2 Ibid., p. 22. 
