﻿334 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Juue 25, 



the vicinity of Singapore, for the water-worn pebbles of the conglo- 

 meratic beds entirely resemble, in their variable size and occasional 

 deficiency of abrasion, the gravel at present accumulating in the vici- 

 nity of the sea-cliffs. The mode in which they are disposed shows 

 that they were from time to time driven and irregularly heaped by 

 violent currents or waves. 



All the sedimentary beds of the district form one series accumu- 

 lated from the debris of the same rocks, and the region underwent no 

 violent upheaval during the period of their deposition. This is an 

 inference from the generally uniform mineral character of the beds, — 

 particular kinds of clay or shale prevailing everywhere, and the con- 

 glomerate layers, wherever they reappear, exhibiting the same pecu- 

 liar clayey matrix and the same prevailing pebbles. No instance of 

 unconformable stratification has been observed. 



The ancient land consisted chiefly of two rocks ; 1st, a fine, tough, 

 easily frangible clay, of which the prevailing colour was a dull violet ; 

 2nd, a granite composed of quartz, chlorite, white felspar, and a fine 

 silvery talc, the last sometimes wanting, and all the ingredients appa- 

 rently varying greatly in their relative proportions at different places. 

 The first rock, reduced to sediment, produced the shales and clays of 

 the district, and, in rolled fragments, furnished a portion of the peb- 

 bles of the conglomerates. The second rock, disintegrated and par- 

 tially decomposed, produced by its debris the great bulk of the con- 

 glomerates, of which the matrix is generally quartz-granules mixed 

 with more or less of chloritic or steatitic earth with greenish and yel- 

 lowish hues. It also furnished a few shale-beds in which chlorite is 

 contained. The quartz-pebbles, generally whitish, but sometimes of 

 black and other colours, were probably derived from this granite also, 

 the quartz in some specimens tending to segregate. It probably ex- 

 isted likewise in contemporaneous veins and nodular masses. The 

 granite, where free from chlorite or the larger developments of quartz, 

 furnished the granules of the sandstone-layers ; or these may have 

 resulted from a more thorough decomposition of the granite, and the 

 washing of the chlorite and felspar to a distance from the place where 

 the sand accumulated, just as we see, at present, partially angular 

 and rolled fragments accumulating in the vicinity of wasting points, 

 the more finely disintegrated sand carried to some distance and accu- 

 mulated by itself, and the clay suspended and deposited over a far 

 wider surface, extending to a considerable distance. 



4. The rocks of this ancient tract differed from the existing phi- 

 tonic rocks of the district, and the latter were not in existence at the 

 time of the deposit of the sedimentary beds, for no fragments resem- 

 bling them have been found in these beds, and many of the rocks 

 which most abound in them nowhere exist in the present plutonic 

 rocks. The most conclusive fact is the entire absence of iron-masked 

 pebbles or fragments in the sedimentary strata. The abundance of 

 ferruginous walls in the latter and in the decomposed plutonic rocks, 

 and the constantly recurring layers of ferruginous pebbles and blocks 

 in the modern debris on the surface of the land and along the shores 

 of the wasting points of both formations, prove that beds derived 



