﻿340 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 25, 



laterite is produced. Sometimes this structure is seen continued from 

 the bed of sandstone into the clay, where the ferruginous ramification 

 and blotches become softer and admit of being cut by the hoe. 



In some places the iron has not pervaded the sandstone, but only 

 penetrated it in layers or veins. In these cases it has disintegrated 

 into a soft ferruginous sand. Where the iron has been diffused the 

 sandstone is undecomposable, and remains hard but brittle. This 

 locality exhibits, 1 st, solid, compact, shining ore ; 2nd, cellular ore 

 filled with decomposed syenite ; 3rd, variously iron-masked sandstone 

 and grit. 



I have hitherto proceeded on firm ground, but, in extending these 

 deductions much further, must take a direction where many may not 

 be disposed to follow, and where we cannot yet hope to obtain a sure 

 footing. I venture, however, to suggest as hypotheses deserving of 

 deeper investigation the following additional views which my obser- 

 vations strongly tend to support. 



Whether the plutonic rocks are simply the product of a heat above 

 the melting-point, or were formed at a lower temperature by chemical 

 and electrical action induced by the heat, the sedimentary rock in 

 contact with and raised upwards by them must have been partially 

 reduced into the plutonic mass. In either case, the upper portion, 

 at least, of that mass is a recomposition of the lower part of the sedi- 

 mentary rock, with an addition of new ingredients from below ; be- 

 cause, so long as the heat was so intense as to produce perfect mix- 

 ture, agitation, and motion inter se of the reduced matter and the 

 plutonic mass into which it entered, the upper limit of the bubble 

 must still have been distant. So long as this level was not reached, 

 each successive portion or layer of the sedimentary ceiling must have 

 passed through similar changes before it became obliterated by com- 

 plete absorption into the plutonic intumescence, ■ — first becoming 

 affected by the mechanical pressure, and then by the increasing heat 

 and exhalations of the labouring mass below. Therefore, at what- 

 ever level the plutonic force, whatever its precise nature may have 

 been, ceased to assimilate the superincumbent rock, this rock, to a 

 certain distance above that level, must have passed through the same 

 stages of alteration, exclusive of the ultimate one, which the plutonic 

 mass in contact with it had itself gradually undergone. Whatever 

 changes we can now observe in the remaining sedimentary rocks ad- 

 jacent to the plutonic bosses, we may conclude that the plutonization 

 of the latter commenced in the same way ; and this we may do with 

 perfect confidence, when we find that these changes are seen over a 

 great region. If these postulates be well-founded, the pheenomena of 

 the district of the Singapore Straits, which are repeated throughout 

 the whole chain of the Malay Peninsula and its prolongation to Banka 

 and Billiton, disclose to us this fact, that the conversion of the sedi- 

 mentary into plutonic rocks began with their being pervaded, in 

 fissures and lines of inferior cohesion, with ferruginous exhalations, 

 producing ferruginous walls and veins. 



Since in the now solid plutonic rocks we find similar walls and 



