114 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
Bay (Bowden) formation of late Oligocene age. If this hypothesis is 
true, then the Low Layton rocks were made before or during the Mont- 
pelier epoch and previous to the Bowden Oligocene. Further research 
is necessary to determine this question finally. In any event, the Low 
Layton “volcano” represents the latest of the igneous rocks in Jamaican 
history, and nowhere are there evidences of further vulcanism. 
Metamorphic Influences of the Tertiary Intrusives. — The intrusion of 
these granitoid and dioritic rocks into the strata of the Blue Mountain 
Serios and lower part of the Oceanic Series has locally produced exten 
sivo metamorphism of the adjacent rocks, baking the shales into hard 
friable slates, and indurating the Cretaceous limestones. According to 
Sawkins,! even the white limestone in St. Catherine “is so completely 
metamorphosed as to be entirely different from the ordinary type.” The 
Jamaican geologists have also asserted that in places the shales have 
been converted into porphyries? and the limestones into serpentines. 
We are not prepared to affirm or deny these assertions.’ 
In localities where the metamorphism and alteration of the Blue 
Mountain Series has been extensive, the Jamaican geologists have re 
ferred to the rocks under the formation name of the “ Metamorphosed 
Series," which they have distinctly defined * as “ conglomerates, shales, 
sands, and limestones, that have undergone various changes by the in* 
trusion of igneous dikes.” It is evident from their descriptions, as pre 
viously noted, that they did not intend to give those rocks a definit? 
place in the Jamaican section otherwise than contemporaneous with the 
conglomerates, shales, and Cretaceous limestones of the Blue Moun? 
tain Series im general; but the editors of the final table in the Re 
ports, and of the general geologio map and sections, have given this 
series a definite position in the geologic section below the “ Hippurité 
limestone” and above the “granite and syenite,” thereby or sating the 
erroneous impression that the metamorphosed beds constitute a distinct 
formation. 
1 Jamaican Reports, p. 147. 
2 Tbid., pp. 62, 188. 3 Thid., p. 62. 
4 Tbid., p. 41. See also p. 105 for a similar definition. 
5 Ibid., p. 841. 
