﻿1851.] LOGAN — GEOLOGY OF SINGAPORE. 321 



Peroxide of iron (containing 50 parts of metallic iron) 80 



Silica, lime, and alumina 5 



Water 15 



Sp. gr. 3-12. 



Pyrites occur very rarely, as I have only observed them in a con- 

 siderable nidus amongst the shale of Pearl's Hill in a mass of anthra- 

 cite, in steatite at P. Piel Ayem, and in the granite of Pulo Ubin. 



4. Alluvium. — All the valleys are filled up to a greater or less 

 height with alluvium, the bulk of which has been deposited from salt 

 water, the freshwater deposits being generally superficial, although in 

 some places of considerable depth. As this formation, in all its 

 varieties, is still going on before our eyes, I will here mention causes 

 and effects together. It has been remarked, that, when the district 

 attained its present level, the sea must have flowed up the numerous 

 long inlets which everywhere penetrated the land. All the different 

 rock-formations must then have been accessible to the sea. Let us 

 revert to this period in Singapore, where we can easily trace our way 

 back to it. At that time, in crossing from Batu Blyer to Tanjong 

 Tanguloh eight arms of the sea had to be passed, each with its shores 

 winding round the points and into the concave recesses of the rami- 

 fying ranges which separated them, and receiving from the multitude 

 of hillocks the clay which every shower of rain removed from their 

 surfaces. The whole land was so constructed as to allow the greatest 

 amount of waste to take place under ordinary atmospherical erosion. 

 Scarcely any flat ground existed. Everywhere acclivities rose from 

 the sea only to attain a certain height and be again bent into declivi- 

 ties which sunk into the sea on the other sides. The upper part of the 

 valleys filled rapidly with clay, mud-flats were formed there and along 

 the margins of the inlets, on which the mangrove and other salt-water 

 trees flourished, and by their decay gave a carbonaceous character to 

 the mud. In the shade of these maritime forests the kapiting and 

 udang kiteh* built up their pyramids of mud and helped to elevate 

 and consolidate the floor, while their excrements and remains, with 

 those of numerous crabs and testaceous mollusks, contributed with 

 the vegetable matter to give a new character to the clay. In the 

 meantime the same process went on in the eastern part of the island, 

 but the sediment there was more mixed with sand. The points at 

 the mouths of the inlets along the whole northern coast of the second 

 basin of the Straits then consisted of sedimentary strata, exposed to 

 the action of waves and currents, and those in the east, in particular, 

 formed of yielding sandstone, supplied a large quantity of alluvial 

 matter, while the shales of the hills near the site of Singapore town 

 freely gave their loose red soil to the sea. When the mangrove- 

 marshes, with their mud-flats in front, had gradually approached the 

 mouths of the narrow inlets, a new condition of things arose. The 

 sand, no longer sinking into deep water beyond the influence of the 

 powerful surface-agitation of the sea, was thrown upon the mud-flats, 



* Burrowing crabs. The udang Jciteh is shaped like a scorpion, and greatly 

 resembles, if it be not identical with, the Thalassina scorpionoides. 

 VOL. VII. — PART I. Z 



