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In order to account for such a succession of events, we may imagine, first, the bed of the ocean to be the receptacle for ages of fine argillaceous sediment, brought by oceanic currents, which may have communicated with rivers, or with part of the sea near a wasting coast.
These different forms of fossilisation may easily be understood if we examine the mud recently thrown out from a pond or canal in which there are shells. If the mud be argillaceous, it acquires consistency on drying, and on breaking open a portion of it we find that each shell has left impressions of its external form.
And later still, Mr Leon, another missionary, heard of the N'yanza and the country Amara, near which he heard the Nile made its escape. Going on with the march we next came to Ndongo, a perfect garden of plantains. The whole country was rich most surprisingly so. The same streaky argillaceous sandstones prevailed as in Karague.
There is one, however, which is peculiarly distinct, admits of sufficiently accurate description, and contains circumstances from which conclusions may be drawn with clearness. This is the ironstone, which is commonly found among the argillaceous strata, attendant upon fossil coal, both in Scotland and in England.
If we take fragments of many other argillaceous grits, retaining the casts of shells, and plunge them into dilute muriatic or other acid, we see them immediately changed into common sand and mud; the cement of lime, derived from the shells, having been dissolved by the acid. Traces of impressions and casts are often extremely faint.
This material of our smooth green mountains may be termed an argillaceous schistus; it has generally calcareous veins, and is often fibrous in its structure resembling wood, instead of being slatey, which it is in general. There is however another species of schistus, forming also the same sort of mountain; it is the micaceous quartzy schistus of the north of Scotland.
These dunes range westward from the coast, which is twenty miles distant, to far inland, in lines parallel to the valley; they are separated from each other by argillaceous flats, precisely like those on the northern shore of Bahia Blanca.
There is a mountain called Guning Pandan, about eighty miles inland; from this branch out three rivers one leads to Mompava, one to Batu Bulat near Tanjong Mora, and one to Landa; the whole intermediate area between the above rivers is of a firm yellow argillaceous schistus, or ferruginous quartz, interspersed with horn and vitreous ores, of a remarkable dark reddish color, abounding with the richest veins of gold, and equal if not superior to any mine extant.
I believe this splendour, commonly reddish but sometimes silvery, to be a reflection produced by large plates of talc, or by gneiss passing into mica-slate. The whole of this country contains granitic rocks, on which here and there, in little plains, an argillaceous grit-stone immediately reposes, containing fragments of quartz and of brown iron-ore.
Bluish-gray limestone, containing corals; mottled limestone, charged with slates, flint, and chalcedony; red, brown, and blue limestone, mixed with red, green, and yellow shales; sandstone of all tints, white, brown, ochry, dark red, speckled and foliated; coarse silicious sandstone, and red quartzose sandstone beautifully veined with purple; layers of conglomerate, of many colored shales, argillaceous iron, and black oxide manganese; massive black and white granite, traversed by streaks of quartz and of red sienite; coarse red felspathic granite, mixed with large plates of silver mica; such is the masonry and such the frescoing.
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