of which such gravel as we are now speaking of might be produced. These strata seem to rise up from under the secondary, where they are intersected by the road; and, for as much as appears, are not of great thickness, so that they cannot have afforded the materials of this gravel directly, though they may have done so indirectly, or through the medium of the red sandstone; that is to say, a primary rock of which they are the remains, may have afforded materials for the gravel in the sandstone; and this sandstone may, in its turn, have afforded the materials of the present soil, and particularly the gravel contained in it.

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Pudding-stones being very liable to decomposition, have probably, in most countries, afforded a large proportion of the loose gravel now found in the soil. The mountains, or at least hills, of this rock, which are found in many places, prove the great extent of such decomposition. Mount Rigi, for instance, on the

side of the lake of Lucerne, is entirely of pudding-stone, and is 742 toises in height, measured from the level of the lake. By the descriptions given of it, as well as of other hills of the same kind in Swisserland, we may, without due attention, be led to suppose that they are entirely formed of loose gravel. Even M. Saussure's description is chargeable with this fault; though, when attended to, it will be found to contain a sufficient proof that this hill is composed of real pudding-stone. The nature of the thing also, would be sufficient to convince us that a hill, more than 4000 feet in height, could not consist of loose and unconsolidated materials.

"If then we regard Mount Rigi as the remains of a body of pudding-stone strata, we must conclude that these strata were originally more extensive; and the adjacent valleys and plains will serve, in some degree, to measure the quantity of them which time has destroyed."*

• Playfair, 373.

The novelty of the topic, in a professed work of this nature, will be a sufficient apology for the length of these introductory observations: but it is now proper to pur sue the plan proposed, by an arrangement of the chief decomposed rocks.

NOME I. DECOMPOSED BASALTIN.

The German mineralogists have not been deficient in their observation of this curious appearance. Karsten, in his catalogue of Leske's collection, has the following instances, among others, in the geographical series.

HYPONOME I.

Basaltin.

"1525. Very fine splintery basalt, with half of Germany. decayed chrysolite disseminated, and exteriorly decomposed to yellowish brown clay, from Rietstein, Saxony.

"1533. Basalt, in which the chrysolite is become very steatitical through decay, from the same place.

"1534. A piece of basalt with decayed chrysolite, wherein it is quite evident that the pores originate from the decay of the latter, from the same place.

"1577. A piece of basalt, mixed partly with small grained chrysolite, partly with felspar, which, as is very frequently the case in granite, is decomposed to lithomarga; from Wachberg, beside Hartmansdorf.

"1667. Perfectly decayed basalt, which in some places contains a large quantity of earth resembling bole, with interposed basalt consisting of lamellar distinct concretions.

"1671. A pentahedral columnar tolerably large piece, which consists entirely of this earth, so that evidently the basalt must have been decomposed into it.

"Rem. It deserves to be noticed as a singular phenomenon, that a perfect hexahedral prism of chrysolite occurs in it.

"1819. A very decayed porous basalt fragment, which lay between the solid layers, and is called lava flag.

"1673. Very decayed porous basalt, which had better be called a basaltic amygdaloid, wherein are still contained abundant vestiges of the earth, with which these pores were formerly filled.

"1674. The same fossil, but the pores, not so uniform, are smaller and larger promiscuously. "1675. The same fossil, penetrated more uniformly with the sulphur-yellow argillaceous mass, which gives to the whole, in the opinion of many geologists, a volcanic appearance."

Amygdalite.

HYPONOME II.