﻿338 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 25, 



have been continued into these strata also. The contemporaneity of 

 the ferruginous dykes is further proved by the mode in which they 

 are connected with the adjacent granite in localities, such as the coast 

 of Batam and the Water Islands near Malacca *, where they can be 

 examined in the undecomposed rock. 



16. The more highly ferruginous parts of the walls in the plutonic 

 and sedimentary rocks are identical in appearance, the proportion of 

 peroxide of iron which they hold being so great as entirely to disguise 

 the original rock. The peroxidation of the iron tends to obliterate 

 all traces of its original condition, and to give a uniformity of aspect 

 to all the rocks which I have designated as iron-masked f, so that we 

 shall not be able to see in what form the iron exists prior to the ex- 

 posure of the rocks to atmospherical influences, until we have much 

 deeper sections than are anywhere exposed at present. It is ob- 

 vious, however, that the effect of decomposition has been to satu- 

 rate the water in the rock with oxidized iron, and diffuse it more uni- 

 formly through the arenaceous and aluminous matter of the walls. 

 If the oxidized crust of the district, which probably descends to a 

 considerable depth, were pared off, the peculiar aspect and structure 

 of the iron-masked rocks would disappear ; the deep rusty, dark brown 

 and black colours, and the scoriform, vesicular, and tubular struc- 

 ture of the walls and lateritic patches, which now so powerfully arrest 

 the attention, would be nowhere recognized, and in place of them we 



* Malacca, including Naning, in all its main features, is identical with the 

 district of the Straits of Singapore. All the phenomena of elevation, ferrugina- 

 tion, &c. which we see here are there repeated. See 1 Five Days in Naning,' by 

 J. R. Logan, Esq., Journ. Ind. Arch, (for May 1849) vol. iii. p. 282. 



f " The interest which the discussions respecting laterite have given to that 

 rock tends to invest it with undue importance geologically. The ferruginous 

 emissions have penetrated all rocks indiscriminately, and their action on sand- 

 stones, grits, and conglomerates is as well-marked as that on clays, marls, and 

 shales, although the latter only produces proper laterite. Even in the clays, 

 laterite denotes one only of many degrees and forms of alteration. To express 

 the origin of these rocks, and its unity, to record the cause of the difficulties which 

 they have presented, and to distinguish them from true metamorphic rocks, I would 

 propose, avoiding any new technical names, to term them simply the iron-mas?ced 

 rocks of the Indo-Australian regions. This term will include the principal or pluto- 

 nically ferruginated rocks, which, without being either completely reduced or meta- 

 morphosed, have been either wholly disguised or partially altered by ferruginous 

 emissions, which have saturated them in the mass, or only affected them in fissures 

 and seams, or have been interfused between portions of the rocks not actually sepa- 

 rated by fissures, but intersected by planes of mere discontinuity, the sides of which 

 have an imperfect cohesion, or having a common border of inferior density and 

 increased porosity, caused either by interruptions in the original deposition of the 

 matter of the rock, or by unequal stretching, or incipient cleavage. The term 

 may be also extended, perhaps, to those sedimentary beds in which the iron-satu- 

 ration, although coseval with the deposit of the other constituents of the rock, has 

 served to obscure or conceal their true nature as well as the derivation of the beds 

 themselves. These beds appear to have been sometimes formed by superficial 

 layers of gravel, &c. being permeated by iron- solutions. With these must not be 

 confounded the broad bands lying over and beside the heads of iron-masked dykes, 

 and which, having been in a loose gravelly or fragmentary state at the time when 

 the plutonic emissions passed through them, became converted into hard, and oc- 

 casionally scorious, ferruginated conglomerates, &c, and are therefore proper plu- 

 Jonically iron-masked rocks." (Journ. Asiatic Society (Calcutta), vol. xvi. p. 521.) 



