130 
Geological Observations made on a 
[May, 
alluded to ; and we find blocks of a reddish brown slaggy looking stone here and 
there, from which they have evidently been derived. These pieces have, I believe, 
been called clay ironstone, a mineral quite different from the clay ironstone which 
is found in the English coal districts. It is about the sp. gr. of 2.8, and seems to 
have been produced by the decomposition of granite, with, perhaps, some magnetic 
iron. The slaggy appearance is occasioned by its numerous irregular hollows mam- 
mellated inside, and indeed some specimens shew much of a stalactitic form. Many 
grains of quartz are imbedded in it, and the quartz gravel of the granitic soil often 
has an iron black or red coating, which shows it to have had a similar origin. 
Those who remember the decomposing state of granite in the neighbourhood of trap 
rocks will not be at a loss to account for this ; to those who do not, I will refer to Dr- 
Daubeny’s work on volcanos, where he states, that in granitic countries which 
are or have been subject to eruptions, the felspar and mica of the rock is in a rapid 
state of decomposition, owing to the carbonic acid gas, which is every where forced 
through fissures in the rock. This is called by the French, the “ maladie du grand," 
and we see that our granite here has, some time or other, been doubled with a 
“maladie,” and a wide spreading one too, so that we may reasonably infer that it has 
suffered from the same cause. The iron-stone itself, from its mammellated and im- 
perfect stalactitic form, seems to have been at least semifluid ; and from its 
softness and earthiness, can only have been a deposit from water. So that if we 
conceive a spring to have issued from the rock, bringing with it this iron clay as a 
sediment, which gradually agglutinated together, and hardened, we might expect to 
find such appearances as we now see. I two or three times came to places where 
this iron-stone seems to have cut through the granitic rock as a vein ; at least it 
formed a reddish streak or band on the surface, for some distance through the 
whitish grey debris of the gneiss j but there were no means of ascertaining its con- 
nection with the solid rock. About four miles to the south of Bancureh, a path- 
way, in the jungle, crosses a considerable mass of it, for near a quarter of a mile. 
Loose blocks of it cover the surface, and in some spots we stand ankle-deep in the 
globular gravel ; but beneath the roots of the grass and bushes, it is solid as far as 
could be determined. A pathway which ran parallel with the first, at the distance of 
4 or 500 yards, gave another sight of it, but the soil and thick vegetation, prevented 
my tracing it further. We cannot, therefore, know whether it continues across the 
country as a dyke, or is merely here in the mass. 
There is another substance which confirms our conjecture respecting the origin 
of this iron-stone. And that is the “ Kankar” or limestone, of which pieces are 
every where scattered through the soil. These pieces are usually from the bigness 
of a walnut to three or four times that size ; but they are not such pieces as would 
have come from the breaking up of a solid bed of carbonate of lime • they are full 
of irregular hollows, which are sometimes faintly mammellated inside They are 
covered with a whitish or yellowish white powder, but the fresh fracture is of a 
brownish grey colour, and the stone compact, and somewhat harder than common 
chalk. The newly exposed cavities inside are lined with minute crystals The irre- 
gular almost dendritic form of these pieces, and the hollows, which abound i» 
them, lead us to believe that they have been deposited round othersubstances, either 
in a vein of the rock or at the surface. 
Those familiar with the productions of what iscallcd a “ petrifying spring,” or, in 
that fb gUa f SC ’ a ” cncr " st '"g calcareous spring, will hardly hesitate to believe 
that they are fragments of such incrustations Th P v • o 
and in these, as also in the iron-stone soil . 7 gl ' amS ° f qi ’ 
wilich look like mica. ’ minut esilvery specks are to be observed, 
