Page:Journal of the Straits Branch of the Royal Asiatic Society (IA journalofstrait121878roya).pdf/42

14 Briefly described then, this district consists of an ancient compact blue Limestone (Paleozoic?) on which is superimposed unconformably a thick series of sandstones, conglomerates, and clay-shales, constituting the most extensive series of beds in this part of Borneo; and on these last lie strata of clay-shales, alluvial clay, river gravels, &c., of very recent origin. Piercing the limestone and sandstone, we find granite and a variety of igneous and trappean rocks—basalt, porphyrite, greenstones, &c., these latter being developed in great abundance in the Antimony districts, where they are in immediate contact with the limestone. The latter formation, in which the lodes of Antimony are seen in situ, is locally rich in fossil organic remains, but I am unable to say whether they have been examined by a competent paleontologist with a view to approximate the age of the rock; the planes of stratification can seldom be made out with any approach to certainty, but where they are evident, they show that the originally horizontal beds have been up-tilted almost on end and much denuded; and there is abundant proof that a very considerable interval in time elapsed between the close of the limestone formation, and the commencement of the succeeding sandstone series.

The sandstone shales have also undergone much disturbance all over this portion of Borneo, although, like the limestone, sometimes retaining their horizontality. They are generally impregnated with per-oxide of iron, and as is so often the case with such rocks, seem quite barren of fossils, except in the coal-measures. It is in this formation that the cinnabar deposits of the country occur.

Both limestone and sandstone have been enormously denuded, the latter rising in isolated tabular mountains, or short peaky trends, with an altitude above the sea varying from 1,500 feet and separated by undulating valleys, in which the limestone appears, sometimes in low hilly træts varying from 200 to 1,200 feet in elevation, sometimes in solitary crags, but invariably with long lines of old sea-cliffs and bald scarps. When accident removes the veil of dark green jungle from their faces, they present to view surfaces fretted by a thousand deep rifts, and fissured and jointed in every imaginable direction.

In the intervening lowlands we have uniformly a deposit of dark yellow felspathic clay, apparently unstratified, and varying in depth from a few feet to 80 feet or more, which is derived from the degradation, and, I think, decomposition in situ, of the clayey sandstones, clay shales, and, especially, the felspathic