intrusive rocks of igneous origin, so abundant in the district. Associated with this clay, and mostly of more recent date are superficial deposits of puddingstone, river-gravels, &c.
The intrusive igneous rocks appear indiscriminately all over Upper Sarawak as mountains and hills, and very commonly in the form of dykes, which, with some few reefs of siliceous veinstone, seam the country in great numbers between the more elevated masses. They consist for the most part of varieties of porphyrite, very decomposable, and more seldom of basalt. The volcanic action which caused their eruption would seem to have been in operation at a period subsequent to the formation of all the stratified sedimentary rocks of the district, and antecedent to only the most recent of superficial deposits. It is in immediate connection with these rocks that we find the deposits of antimony, arsenic, and cinnabar; and as there is reason to believe that they occupy fissures caused by the eruption of the volcanic rocks, and that their deposition took place after the cessation of volcanic action, we arrive at a remarkably recent date for the formation of the mineral lodes at Upper Sarawak.
Such in outline are the geological features of Upper Sarawak. Other formations and many other varieties of rocks, are to be met with in the Territory, but it is not necessary to particularise these, as they are not connected with the mineral deposits of the country, so far as we know, and are therefore foreign to the subject of these notes.
The minerals and mineral ores of Sarawak, in relation to their local distribution, may be summarized as follows, the names of those which have only been observed in traces being italicized.
District of Sarawak Proper (including Lundu and Samarahan),—Gold, Antinony, Arsenic, Argentiferous-Arsenic, Cinnabar, Cobalt, Nickel, Manganese, Copper, Iron Diamond, Aquamarine, Coal.
- District of Sadong.—Gold, Coal, Diamond, Iron, Cinnabar.
- District of Batang Lupar.—Gold, Coal, Iron, Antimony.
- District of Rejang.—Coal, Iron, Arsenic, Antimony, Nickel, Gold.
- District of Mukah and Bintulu.—Coal, Antimony.
In the districts of Saribas, Kalakah and Oyah, I have no reliable information of the occurrence of useful minerals. A number of the above mentioned species are known to have been detected in other parts of N. W. and W. Borneo beyond the limits of the Sarawak territory, viz., Gold, Antimony, Arsenic, Copper, Cinnabar, Iron, Diamond, and Coal, some in work-
