1847.] including Notices of Sumatra, the Malay Peninsula, fyc, 631 



may pass without disturbing the internal arrangement, because the 

 motive force will meet with an equal resistance throughout. But where 

 the mass acted on suddenly changes from a dense to a lighter rock, 

 fractures and other internal disturbances will follow according to the 

 intensity of the force, and where the mass of rocks is met externally by 

 the rare elastic mass of the atmosphere, the resistance in that direction 

 being removed per saltum, the general centrifugal tendency which will 

 be impressed by the nether forces, even when their proper direction 

 is more horizontal than vertical, will cause the upper rock to a certain 

 depth to be fractured, loosened and expanded, the external fragments 

 and particles being perhaps quite free and even projected. In this 

 condition the whole superficial mass will readily yield to continuing 

 vibratory action, and any or all of the phenomena above described may 

 be the result. It is a further argument in favour of mechanical con- 

 vulsions of considerable violence and irregularity, that although the 

 general dip of the strata of Singapore be from westerly to easterly, cases 

 are found of a hill resting on the same apparent base with an adjoin- 

 ing one where the general rule operates, having its strata inclined from 

 east to west, and even in the same hill particular sides or outlying 

 ridges or spurs, present deviations both in the direction and in the 

 angle of the dip. 



5. — Volcanic Action. 



Hitherto we have remarked no phenomena that may not be referred to 

 the ordinary mechanical or chemical forces acting at the surface of the 

 earth, or to critical mechanical disturbances. But I have now to notice 

 a large and varied class of facts which require different forces to be 

 introduced. These facts are so numerous, so constant in their occur- 

 rence over every part of the Island which is open to examination, and 

 not less than elsewhere in those parts from which the observations of 

 writers on the geology or mineralogy of Singapore have been drawn, 

 that it is difficult to conceive through what fatality they have hitherto, 

 for the most part, escaped notice or been passed over as unimportant.. 

 The most obvious of these facts are dykes and veins of igneous rocks, 

 masses in situ and scattered fragments of rocks, such as sandstone, 

 clays, shales, granite, &c, altered by the action of fire ; rocks in veins and 

 joints often highly indurated, whereby sandstone has acquired sometimes 

 a cellular structure, and at other times externally a honey-combed 



