30 



therefcre, that the jointed structure of rocks will be found to be much more connected 

 with the directions' in which igneous rocks have swelled up and been injecfcd, and islands, 

 mountains and continents been consequently upraised, than with the magnetic meridians. 

 If due to mere tension , it may have originatcd under both or one of two influences. If 

 we conceive , what is most reasonable and consistent with observation , that the formation 

 of mountain chains is accomplished by a slow movement or succession of movements prolong- 

 ed during a great geological period , then we must admit that the upper layers of the 

 gradually ascending and cooling mass have been exposed to continued or repcated pressure 

 from below , which, of itself, would cause the partially harden cd or viscid crust to crack, 

 or would give rise to planes of inferiour resistance to tension in which the mass would have 

 a tendency to part. But there is another source of tension which may co-operate with exter- 

 nal pressure, or exist independently of it, and that is simple contraction after crystalliza- 

 tion on cooling. 



In and near Singapore we find the stratified rocks in general elevated into low ranges of 

 hillocks, of which the axes coincide with that of lhe Malay Peninsula and the Islands 

 from Singapore to Banca. The strata have commonly been til led up at very high angles, 

 frequently approaching vertical. Considering the Peninsula and its prolongation in the 

 Archipelagoes soulh of Johore as one band which has been subjected to elevatory plutonic 

 forces (1) , the first external effect of these forccs must have been to cause a great tension 

 from NE. to SW. , across the zone, followcd by a rending and displacement of the 

 superincumbent strata, and injection of ignifluous matter along lines at right angles to 

 that of tension , or from NW. to SE. The principal divisional planes must have been 

 the result not of a transverse tension like the first, but of a subsequent longitudinal 

 one (2), 



The great rending and displacement of the strata , and the circumstance of the heads of 

 adjoining strata being sometimes broken up and intermingled , prove that mechanical 

 movements of great violence , and combining a horizontal vibratory with a vertical 

 action , must have attended their upheaval. The direction of these movements must have 

 agreed with the line of tension , because they were nothing more than the effect of the 

 tension reaching the limit which the rocks subject to it could bear. The strata are generally 

 inclined from SW. to NE. , alt hou gh there are several exceptions. The elevatory force 

 therefore acted, to a certain extent, in this direction. Was there an actual propulsion of the 

 fluid or viscid matter from SW. to NE. or merely an undulaling motion in this direction? 

 Such a motion is even now experienced in a slight degree along the western border at least 

 of the Peninsula when the subterranean forces are acting beneath the western border of Su- 



(1) Whether a simultaneous action elevated both the central granitic chains of the Peninsula and the «emi- 

 volcanic hills along Iheir base and to the south of the Peninsula, or the latter were due to a later subsidiary 

 action connected with the shifling of the subterranean forces to Sumatra , does not affect the abore reasoning , 

 since the fact of agreement in direction is clear. 



(2) See Mr. Hopkis's papers, Reseavches in Phytical Geology Are. 



