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Updated: May 14, 2025
The grassy roadway would certainly encourage the supercilious beasts to proceed in the desired direction. The shelters were in a very ruinous state. They were made of rough, scoriaceous lava rocks. The circular enclosures varied from 8 to 25 feet in diameter. Most of them showed no evidences whatever of recent occupation. The smaller walls may have been the foundation of small circular huts.
I can understand these facts, namely, the blending of the jasper into the semi-decomposed basalt, its occurrence in angular patches, which clearly do not occupy pre-existing hollows in the rock, and its containing little vesicles filled with chalcedony, like those in the scoriaceous lava, only on the supposition that a fluid, probably the same fluid which deposited the chalcedony in the air-cells, removed in those parts where there were no cavities, the ingredients of the basaltic rock, and left in their place silica and iron, and thus produced the jasper.
Their constituent minerals had ample opportunity to sort themselves and crystallize from the fluid mixture, and none of that mixture was left to congeal as a glassy paste. They consolidated also under pressure. They are never scoriaceous, for the steam with which they were charged was not allowed to expand and distend them with steam blebs.
At the east side of the lake we find a stream of scoriaceous lava of a purple or reddish colour, highly vesicular, and containing crystals of mica; but the most important lava-stream is that which has taken a southerly direction from the crater of the Laacher See towards Nieder Mendig and Mayen, for a distance of about six miles.
Gases and steam escaping from other similar masses may leave them hollow, when they are termed bombs, or may pit their surfaces with irregular bubble-cavities, when they are called scoriae or scoriaceous.
The fragments consist usually of different varieties of scoriaceous and compact lavas; but other kinds of rock, such as granite or even fossiliferous limestones, may be intermixed; in short, any substance through which the expansive gases have forced their way.
The angle of this wall is great, and its appearance from below is impressive from its enormous breadth, and its abrupt rise without bend or droop for a good 2,000 feet into the air. It is covered with short, yellowish grass through which the burnt-up, scoriaceous lava rock protrudes in rough masses.
It is clear that the lava once filled the whole valley up to the dotted line d-a; but the river has gradually swept away all below that line, while the tributary torrent has laid open a transverse section; by which we perceive, in the first place, that the lava is composed, as usual in this country, of three parts: the uppermost, at a, being scoriaceous, the second b, presenting irregular prisms; and the third, c, with regular columns, which are vertical on the banks of the Volant, where they rest on a horizontal base of gneiss, but which are inclined at an angle of 45 degrees, at g, and are nearly horizontal at f, their position having been everywhere determined, according to the law before mentioned, by the form of the original valley.
The successive sheets are either closely united together, or are separated from each other by beds of scoriaceous rock and of laminated tuff, frequently containing well-rounded fragments. The interstices of these beds are filled with gypsum and salt; the gypsum also sometimes occurring in thin layers.
The scoriaceous fragments and the calcareous matter are associated in the most irregular manner, sometimes in obscure beds, but more generally as a confused breccia, the lime in some parts and the scoriae in others being most abundant.
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