It is, at present, a perfectly tenable hypothesis that all siliceous and calcareous rocks are either directly, or indirectly, derived from material which has, at one time or other, formed part of the organized framework of living organisms.

[Illustration: SILICEOUS CUTICLE FROM UNDER-SIDE OF LEAF OF DEUTZIA SCABRA.]

[Illustration: SILICEOUS CUTICLE OF GRASS.] 1076.

It is native siliceous oxide of zinc.

This stream must be the Murchison River, as no other was passed for 30 miles to the northward; the effects of violent floods were visible, but it did not bear the character of a stream rising at any great distance inland, nor did the nature of the gravel and sand brought down by it indicate a rich soil on its upper portion, as I did not see anything besides fragments of siliceous rock and garnet sand.

Except on the banks of the river and creeks, the country is very poor and stony; the geological structure of the country is the same as at Sea Rangethe same bands of sandstone cliff resting on soft shales, the strata being horizontal; but beneath the shales chert and coarse siliceous limestone were exposed, and fragments of jasper are frequent.

The upper stratum is a bed of ironstone conglomerate about twenty feet thick, this rests on sandstone, the upper part of which is highly ferruginous, then passes away into a variegated sandstone imperfectly stratified, changing into a hard siliceous sandstone which is white and breaks with a conchoidal fracture; this rests on a hard cherty sandstone similar to that of the Victoria River.

The locality has been remarkable for landslips, owing to the siliceous nature of the soil; I saw traces of a fearful catastrophe of the kind which had, some time before, buried or destroyed many of the houses and their occupants, the enormous mass having also sunk several steam-boats and other vessels which were moored at the foot of the bluff under the town.

The summit of Crystal Head is of flat tabular form; and the sides, which are both steep and rugged, are covered with stunted trees and high grass, now quite dry: the geology of this part is principally of siliceous sandstone; and on the beach we found large detached water-worn masses of the same rock, incrusted with quartz and epidote in a crystallized state. (*Footnote.

The rocks on the hills are formed of a close-grained siliceous sandstone; and the ground is covered with loose masses of the same rock, with spinifex growing between them; this plant is of itself sufficient to indicate the poverty of the soil.

For the siliceous ingredient of his composition he made choice of chalk-flints, calcined and ground to powder.

The mill is a hollow cylinder of wood bound with hoops, and having a bottom of blocks of chert, a hard, tough, siliceous stone: the mill-shaft is perpendicular, and has two horizontal arms passing through it cross-wise.

From his inquiries and observations, Brewster was led to conclude that tabasheer was only produced in those joints of bamboos which are in an injured, unhealthy, or malformed condition, and that the siliceous fluid only finds its way into the hollow spaces between the joints of the stem when the membrane lining the cavities is destroyed or rent by disease.

Near the banks of the Ohio, full three hundred miles from the sea, I found conglomerations of marine shells, mixed with siliceous earth; and in nearly all the runs throughout Kentucky, limestone pebbles are found, bearing the perfect impressions of the interior of shells.

The siliceous ingredient is calcined flint; and in some of the porcelain works, (particularly, I believe, those at Worcester,) the soapstone from the Lizard-point, in Cornwall, is employed.

The rock, a fine-grained siliceous sandstone, is disposed in horizontal strata, from six to twelve feet thick, each of which projects about three feet from that above it, and forms a continuity of steps to the summit, which we found some difficulty in climbing; but where the distance between the ledges was great we assisted our ascent by tufts of grass firmly rooted in the luxuriant moss that grew abundantly about the water-courses.

The geological character of the island is a red-coloured, coarse-granular, siliceous sandstone, disposed in horizontal strata, and intersected by veins of crystallised quartz.

The banks are from two to four hundred feet in height, and consist of close-grained siliceous sandstone, of a reddish hue;* and the view (Plate above) shows that the beds are nearly horizontal, and very regularly disposed; the cascade there represented being about one hundred and sixty feet in height, and the beds from six to twelve feet in thickness.

The summit of the head is flat and tabular, and the rocks in the vicinity are described by Captain King as consisting of siliceous sandstone.

Reddish, coarsely granular, siliceous sandstone; in horizontal strata, intersected by veins of crystallized quartz.

This projection, which we called Eagle Point, is of a siliceous sandstone formation, intersected by nearly vertical veins of quartz, and forms a spur thrown off from a high range four miles to the south-eastward.

The rice kernel is inclosed within two coverings, a course outer husk, which is easily removed, and an inner, reddish, siliceous coating.

When well ground, it can be digested, with the exception of the siliceous coating.

DYNAMITE, a powerful explosive substance, intensely local in its action; formed by impregnating a porous siliceous earth or other substance with some 70 per cent. of nitro-glycerine.

A specimen of the rock, taken from the shore and given me by Lieutenant Yule, is a very curious siliceous breccia; when viewed from the sea I had observed the cliffs to exhibit horizontal and vertical fissuresapparently lines of cleavageas I had seen assumed on various occasions during our last cruise by granite and porphyry.