hill: geology of JAMAICA. 53 



The Kiciimoxd Beds. 



These beds constitute the upper subdivision of the Blue Mountain 

 Series. Their arrangement and composition, consisting of shallow 

 marine deposits of worked over and water assorted terrigenous material, 

 indicate a succession of more quiet sedimental conditions than those 

 which marked the preceding epoch. 



The rocks are mostly black, bituminous, laminated clays, and fer- 

 ruginous sandstones with occasional beds of loose conglomerate. They 

 occur in uniform alternations of thin, regular, and evenly bedded strata, 

 varying from an inch to a foot or more in thickness. They are dull 

 blue-black on fresh exposure, but undergo excessive oxidation and hence 

 are ordinarily of dark brown ferruginous colors. In general texture, 

 arrangement, color, and stratification they resemble the Eo-Lignitic 

 (Lower Eocene) beds of the southern United States. The clays con- 

 tain many small flakes of carbonized vegetal matter, and silicified wood 

 has been found in the gravel. The material is mostly derived from the 

 antecedent beds of the lower division of the Blue Mountain Series. 

 The so called " sandstones " are composed of cemented grains of water 

 worn hornblende-andesite derived from the underlying igneous rocks, 

 and the shales are the same material more finely triturated and mixed 

 with vegetal matter. The conglomerates consist of rounded pebbles of 

 various dimensions, and in places attain a thickness of 50 feet. They 

 are almost entirely of the same material as those of the lower subdi- 

 vision. Rounded fragments of the Rudistean limestone also occur in 

 them. These have been noted first by Barrett,^ then by Sawkins and 

 others of the Jamaican Survey, in the parishes and districts of Port- 

 land, St. James,^ St. George and Metcalfe, St. Mary, and St. Thomas-in- 

 the-Vale. In addition to these rocks of the conglomerate, former ob- 

 servers have noted,* from the bluff at Port Maria, specimens of gneiss 

 and crystalline slates, " rocks of which no trace either in situ or other- 

 wise have hitherto been found in Jamaica ; also a fine-grained granite 

 to which nothing analogous has been noted on the island. ... In this 

 unique collection are many instances of rocks which have totally dis- 

 appeared from the surface of Jamaica, but which must have existed 

 during former epochs, either in the formations of this country or in 

 adjacent lands that have been destroyed." 



At the same locality, as also noted in the Jamaican Reports,* the 



1 Quart. Jour. Geol. Soc. London, 1860, Vol. XVI. pp. 324-326. 



2 Jamaican Reports, pp. 245, 246. 3 Ibid., p. 130. * Ibid., p. 130. 



