Both lime and sandstone have been extensively denuded, and the latter rises in isolated tabular mountains, or short peaky trends, to an altitude occasionally of 1500 feet above the sea, the ridges separated by undulating valleys, in which the limestone comes to the surface. Sometimes these denuded masses form low hilly tracts varying in elevation from 200 feet to 1200 feet; sometimes they appear as solitary crags, but invariably present long lines of ancient sea-cliff, and bold scarped faces, fissured and jointed in every conceivable direction. In the intervening lowlands is a deposit of dark yellow felspathic clay varying in depth from a few feet to eighty feet and more, derived from the degradation of the hills by water. Associated with this clay and of more recent date are superficial deposits of pudding-stone and river gravels. The intrusive igneous rocks show mainly in the form of dykes, seaming the stratified rocks; consequently volcanic action took place subsequent to their deposition, but it was also antecedent to the more recent of the superficial deposits. It is in immediate connection with those plutonic dykes that we find the deposits of arsenic and cinnabar, occupying the fissures produced in the stratified rocks by volcanic upheavals, and we are led to the conclusion that these mineral lodes were deposited after the cessation of the upheaval. Gold occurs in the form of fine sand in the alluvial deposits, and in the gravel of the rivers over a great part of Sarawak; and also in pockets of the limestone, in which it has been allowed to fall by water. Nuggets are of extremely rare occurrence, but Sir Spencer St. John mentions having seen one of seven ounces taken from the auriferous clay at Krian near Bau. The gold dust is usually in a state of finest comminution. So far no gold reef has been come upon.