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Their nucleus is almost as hard as basalt, and they are intermingled with little cavities, owing to bubbles of gas, filled with green earth, and crystals of pyroxene and mesotype. Their basis is greyish blue, rather soft, and showing small white spots which, by the regular form they present, I should conceive to be decomposed feldspar.
C| TUFA AND TRAP. In Londa, the bottom of the valley E| 2500 feet. is formed of ferruginous conglomerate on the surface; N| Lake Ngami. hardened sandstone, with madrepore holes, T| banks of gravel, and occasionally trap; R| south of 12 Degrees, large patches of soft A| TUFA. calcareous tufa, with pebbles of jasper, L| agates, &c., lie on various horizontal traps, | amygdaloids with analami and mesotype, which is P| burst through by basaltic rocks forming hills, L| and showing that the bottom of the valley A| RADIATED ZEOLITE. consists of old silurian schists; T| there are also various granitic rocks E| cropping through the trap.
TAHITI. Passage from wacke into trap; singular volcanic rock with the vesicles half-filled with mesotype. MAURITIUS. Proofs of its recent elevation. Structure of its more ancient mountains; similarity with St. Jago. ST. PAUL'S ROCKS. Not of volcanic origin. Their singular mineralogical composition.
At Bombwe we have the same trap, with radiated zeolite, probably mesotype, and it again appears at the confluence of the Chobe, farther down. As we passed up the river, the different villages of Banyeti turned out to present Sekeletu with food and skins, as their tribute.
This conclusion is not deduced from the observations I made at the southern declivity of the littoral Cordillera, between the Morros of San Juan, Parapara and the Llanos of Calabozo. The greyish blue amygdaloid contains fendilated crystals of pyroxene and mesotype. It forms balls with concentric layers of which the flattened centre is nearly as hard as basalt.
We spent forty-two and a half hours, paddling at the rate of five miles an hour, in coming from Linyanti to the confluence; there we found a dike of amygdaloid lying across the Leeambye. This amygdaloid with analami and mesotype contains crystals, which the water gradually dissolves, leaving the rock with a worm-eaten appearance.
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