﻿320 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 25, 



in walls, veins, and seams. "Where they are most abundant the prin- 

 cipal walls follow the direction of the beds, but are most frequently 

 sinuous, and connected by branches with those adjacent. The beds 

 themselves, in such cases, are generally bent in a similar direction. 

 The sides of the beds, where not obliterated by these walls, are often 

 indurated and acquire a shining mammillated surface. Sandstones are 

 often divided into little cubical and rhomboidal compartments, being 

 pervaded by a complete reticulation of a thin black ferruginous crust 

 or wall, which, from the washing-out of the sandstone by the action 

 of the waves, projects, like the sepiments of a honey-comb, from the 

 surface. 



In clays and shales (and sometimes in fine-grained sandstones) red- 

 coloured laminae are frequently seen in connection with the ferru- 

 ginous walls and veins, and arranged either in lines radiating from 

 points or in concentric curvilinear figures. The most remarkable 

 examples of this laminar coloration occur in the islands of Jong, Sa- 

 hara, and Bukum. Another kind of lamination is often seen in fer- 

 ruginous walls. In this the original laminae of the rock are pre- 

 served, but converted into iron-ore. Sometimes they are swollen into 

 a globular form. This seems to be the origin of most of the mam- 

 millated and botryoidal forms. 



The associated iron and quartz are found developed on the largest 

 scale at Marambong and Tanjong Kinawar ; and more or less quartz 

 is found in almost every highly-ferruginous wall. 



The localities where the iron predominates over the quartz are very 

 numerous. Amongst the more striking instances may be mentioned, 

 in sandstones, T. Sirimbun, Mount Palmer, the coast of P. Tikong 

 Besar ; and in shales and clays, P. Dammar, the coast of Singapore 

 opposite, Tanjong Penjuru, P. Siking, P. Sabaru, the lateritic por- 

 tion of Government Hill, the north-east part of P. Tikong Kichi, 

 and Tanjong Pungai. 



The iron-rock is generally a hydrous peroxide and different forms 

 of brown haematite, compact and ochry. In most localities the pro- 

 portion of iron varies much, and is often too small to entitle the rock 

 to be called an ore, but patches and masses of ore occur abundantly, 

 and some walls are almost wholly composed of it. Regularly crystal- 

 lized ores are not frequent in considerable patches, but heematitic 

 crystals occur in the body of pieces of compact ore ; and the thin 

 brownish-black and black ore penetrating ferruginated rocks in seams, 

 forming the external walls or crust of mammillary and botryoidal, 

 and the lining of tubular and cavernous, masses of laterite and iron- 

 masked rocks, is sometimes composed of fine fibrous crystals. I have 

 found large-crystallized haematite in ferruginous sandstone and shale 

 near the boundary of the plutonic and sedimentary tracts to the west- 

 ward of Bukit Timah, and in violet-coloured shale midway between 

 the Chinese Tokong, on the Pandan, and Bukit Timah. 



We have already mentioned the mode in which ferruginous rock 

 occurs in the plutonic tract. The following is an analysis, made in 

 England, of a specimen of the common ore of the dykes occurring in 

 this tract. 



