﻿1851.] 



LOGAN — GEOLOGY OF SINGAPORE. 



313 



in the alluvial plain forming the districts of Rochor, Gelang, Kalang, 

 Paya Lebar, and Siglap, with its long branches or inlets, extending 

 between the hill-ranges to the middle of the island ; and the latter in 

 Batam and Bulan Bays*. Its greatest length, from the extremity of 

 Batam Bay to that of the Singapore Plain, is about 15 miles f; its 

 least, from Tanjong Siglap to T. Singkwang, about 8f miles ; its 

 breadth is nearly 10 miles. The third basin is the middle of a pro- 

 longed submarine valley which stretches northward into the Penin- 

 sula, where it forms the estuary of the River Johor ; on the south it 

 penetrates the Johor Archipelago, where it forms the Strait of Rhio 

 separating Batam from Bintang. The fourth or most easterly basin, 

 — about 18 miles long, 20 miles broad at its two extremities, and 14 

 miles in its middle, — lies between the south coast of the S.E. pro- 

 montory of the Peninsula and the N. coast of Bintang. 



2. Geological Topography. — In giving a general sketch of the geo- 

 logy we shall consider the District as divided into four zones nearly 

 corresponding with the four basins of the Strait. 



1st zone. — The first, or most westerly basin, has on its southern 

 side a deep channel, free from islands, which opens into the second 

 basin between Pulo Sambo Kichi and Pulo Sikijang. To the south 

 of this channel a dense clump of islands commences, which stretches 

 to the S.E., and includes Bulan with its conspicuous peak, from which 

 the Dutch hydrographers have named the group the Bulan Archipe- 

 lago. It remains to this day unsurveyed and unexplored either by 

 the Dutch or English, and in some charts still figures as one island, 

 although it must consist of several scores J. It is separated by a 

 narrow channel, called Silat Batu Haji, from the west coast of Batam, 

 which has a general direction coinciding with that of this basin. The 

 northern part of the basin is shallow and contains numerous islands ; 

 and the same configuration is continued in the western section of 

 Singapore, which is a congeries of narrow peninsulas, separated by 

 mangrove creeks. The prolongation of the zone in the mainland, 

 including the S.W. promontory, is flat and alluvial towards the W., 

 and hilly towards the E. 



The whole of this zone consists of stratified sedimentary rocks, 

 sandstone appearing to predominate towards the west, and sandstone 

 and conglomerate, intermixed with clay and shale, towards the mid- 

 dle. Towards the eastern side a broad band of shale, chiefly choco- 

 late-coloured, occurs ; and in the extreme east, where it abuts on the 

 syenite of the 2nd zone, this shale is interstratified with sandstone 

 and conglomerate. 



The western portion is nearly all covered by the sea or alluvium, 

 the only islands, except those belonging to Bulan Archipelago, being 

 Pulo Rungkum (Alligator I.), Pulo Sinang (Barn I.), Situmbu Kichi, 



* These bays are deeper than they appear on the map, and the numerous creeks 

 and inlets which pierce the island between the hill-ranges are not laid down, no 

 survey of the bays having been yet made. 



f About twenty-one miles, if we include the valleys which have been inlets of 

 the sea since the land attained its present level. 



X I have examined the northern part, where I found a perfect labyrinth of islets. 



