On some Cretaceous Rocks in the South-Eastern Portion of Jamaica

B elow the thick Tertiary deposits in Jamaica are found thin beds of fossiliferous limestone, underlaid by igneous rocks. These strata form the subject of the following communication. The newest bed of the fossiliferous limestones is exposed on the north side of the Plantain-garden River, three miles west of Bath. This section shows a bed of compact limestone, 8 feet thick, resting on a thick bed of conglomerate, and overlaid by shale. The shale is of a dark colour and without organic remains. The limestone is compact and grey, with thin veins of calc-spar; it contains numerous fossils, all of them characteristic of Cretaceous or other Secondary strata, viz. Inoceramus, Hippurites , and Nerinœa . The conglomerate is composed of rounded pebbles of igneous rocks and a white fossiliferous limestone; it is succeeded by a great thickness of unfossiliferous black shale. A quarter of a mile higher up the river there is a section of some vertical beds of limestone, probably older than the series already described. A bed of conglomerate separates them from great masses of porphyry. This section (see woodcut) exhibits thin bands of limestone, alternating with shale, containing limestone-nodules. Some of the thin bands of limestone are crowded with fossils, principally Inoceramus, Hippurites , and a species of Bulla (?). These fossilfferous beds are succeeded by a bed of conglomerate, 12 yards thick, composed entirely of pebbles of porphyry, identical in structure and colour with the adjacent mass. The conglomerate is not altered at its junction with the igneous rock. The