﻿336 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 25, 



9. One of the most striking characteristics of the district is the 

 protean nature of the plutonic transformations, remarkable alike in 

 the diversity of the plutonic rocks themselves, and in the numerous 

 degrees and kinds of change which the plutonic agency has produced 

 on the strata. There are considerable tracts in which the granite 

 undergoes little variation, but which differ decidedly from each other. 

 There are tracts where the plutonic rock graduates or passes abruptly 

 from large-grained granite to the most finely grained, or, losing its 

 quartz and mica, passes into greenstone or into compact felspathic or 

 hornblendic rocks. Amongst the sedimentary rocks we find that 

 some, near the line of junction with the plutonic, have merely become 

 ferruginous, while others, apparently distant from it, have become 

 highly indurated. The same rock, completely iron-masked at one 

 place, exhibits no change whatever a few feet off. We have seen 

 that the mechanical action to which the strata have been subjected 

 participates in this want of uniformity. 



10. Is the explanation of this character of the district, — the absence 

 of all other sedimentary formations but the existing limited one, the 

 entire disappearance of the ancient rocks which composed the district 

 when the present strata were being formed, and the mode in which 

 the plutonic exhalations have freely risen through the latter, — to be 

 found in the circumstance of the plutonic action having extended to 

 the surface of the ancient land (whether beneath the sea or not is 

 another question) and assimilated it all, excepting a thin crust of the 

 newest and highest beds, or rather bands and patches of that crust, 

 which now lie scattered over the great plutonic mass of the Peninsula ? 

 It is clear that granite does not require a greater pressure for its for- 

 mation than the so-called volcanic rocks into which it passes. In 

 Pulo Ubin and other localities, we see, in the same rock, at one place 

 a perfect granite, composed of large crystals of quartz, felspar, mica, 

 and hornblende, and at another a compact or finely granular green- 

 stone or basalt, so that the granitic form does not necessarily depend 

 on the depth at which crystallization or plutonic metamorphism takes 

 place*. 



11. At the time of the upheaval of the strata they were new, and 

 had neither been consolidated by great pressure nor indurated by any 

 prior plutonic action. Where they have escaped the influence of the 

 ferruginous and siliceous exhalations, and the heat given out during 

 their elevation, the more aluminous beds are still soft clays, and the 

 arenaceous slightly coherent sand, sometimes not distinguishable from 

 the beds of clay and sand forming along the shores at present. 



If the now visible plutonic rocks had been formed at a great depth 

 and under a vast equal pressure, they would have been more uniform 

 in their composition and structure, and in their action on the imme- 

 diately superincumbent strata. They would have more slowly cooled 

 down, and the adjacent strata, long exposed to the heat, would have 

 acquired a certain general induration. If the strata had still been 

 accumulated over the plutonic mass to a great thickness when the 

 latter ceased to reduce them, and been subsequently pared down to 

 * See account of the rocks of Pulo Ubin, p. 22, Trans, Batav. Soc. Arts and Sc. 



