﻿1851.] 



LOGAN — GEOLOGY OF SINGAPORE. 



329 



Straits of Malacca are sheltered by the mountains of the Malay Pe- 

 ninsula, the eastern coast of our district is exposed to the full force 

 of the monsoon, and the hills that stretch along it are not sufficiently 

 high to destroy, although they considerably modify its influence in 

 the Straits. During the greater part of this monsoon rains fall abun- 

 dantly, the streams are frequently swollen, and sometimes overflow 

 their valleys, the sun is obscured more frequently and for longer pe- 

 riods, the temperature is lowered, strong winds often prevail, and the 

 sea is more agitated. It is, therefore, in this monsoon that the ero- 

 sions an. abrasions of the land referable, mediately or immediately, 

 to the climate are greatest. 



The heat and humidity of the climate affect the solid inorganic 

 mass of the land chiefly by their favouring the decomposition of the 

 rocks, the growth of vegetation, and the degradation of the soil. 

 These operations are much less marked than those of the sea, but 

 they are incessantly progressing over the whole land, and their effects, 

 when accumulated by time, must be very great. The soil is always 

 kept moist, which causes the decomposition of the plutonic rocks to 

 descend to a great depth ; and the rain, the most constantly acting 

 and universal mechanical agent of geology, and here gaining a maxi- 

 mum of effect from the configuration of the ground, falls on an ave- 

 rage about half the number of days in the year. When it is con- 

 sidered that every considerable shower in Singapore is the parent of 

 innumerable little rills, — each turbid with fine clay and propelling 

 quartz-granules, &c, — which pour down the sides of hundreds of 

 hills into the valleys, the great beds of alluvial clay appear less dis- 

 proportioned to the size of the streams. These are very numerous, 

 but, owing to the low level of the country, insignificant ; the broad 

 and deep salt-water creeks, which occur at short intervals along all 

 the coasts * and seem to be the estuaries of considerable rivers, seldom 

 extending beyond a few winding reaches, at the top of which they 

 dwindle to petty rivulets of fresh water. None of the Singapore 

 streams have courses longer than six miles, and it is only after heavy 

 showers that they pour down a considerable body of water. The 

 continental part of the district includes one large river, the Johor, 

 the course of which, in a direct line from its source in Gunong Blu« 

 mut to Tanjong Tikong, is about fifty miles ; but it may be said to 

 fall into the sea to the north of the district, because the long and 

 broad estuary as far up as Tanjong GMong is an arm of the sea. It 

 has caused the formation of a large alluvial tract extending along the 

 west side of the estuary. The other rivers of the mainland falling, 

 with one exception, into the Old Straits, such as the Pulai, Sakodai, 

 Tambrau, Libam, and Santi, have all elevated the beds of their valleys 

 to some distance from the Strait to a level between low and high 

 water-mark, and covered them with marine forests. Thus in every 

 valley of the district some of the alluvial processes before-described 

 are constantly proceeding. 



The Straits, as we have seen, are sheltered from the direct influence 



* The eastern coast of the mainland and the S.E. coast of Singapore must be 

 excepted. 



