114 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



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 

 Series and lower part of the Oceanic Series has locally produced exten- 

 sive 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 these rocks a definite 

 place in the Jamaican section otherwise than contemporaneous with the 

 conglomerates, shales, and Cretaceous limestones of the Blue ]\Ioun- 

 tain Series in general ; but the editors of the final table in the Re- 

 ports,^ and of the general geologic map and sections, have given this 

 series a definite position in the geologic section below the " Hippurite 

 limestone " and above the " granite and syenite," thereby creating the 

 erroneous impression that the metamorphosed beds constitute a distinct 

 formation. 



1 Jamaican Eeports, p. 147. 



2 Tbid., pp. 62, 188. 3 Ibid., p. 62. 

 * Tbitl., p. 41. See also p. 105 for a similar definition. 

 6 Ibid., p. 341. 



