“The collections in this city are derived partly from M. Werne, who made them in the expedition sent by the Basha of Egypt in the year 1840, and partly are owing to the scientific liberality of M. Russegger; and they afford sufficient information with respect to the general geognostic relations of these scarcely discovered mountains.
“The chain of the Mountains of the Moon consists, according to the several specimens, of gneiss and mica-slate. One of these specimens, was taken from the most southerly point that the expedition reached, and indeed, ‘from the cataracts in the land of Bari;’ that is to say, from the rock which prevented the expedition from penetrating further into the country. It is gneiss, composed of white feldspar, and much black mica, and mica-slate; the friable and exceedingly granulous quartz does not contain feldspar, but small scaly black mica. There is found, moreover, in the valley of Berri, magnet iron-stone, which, however, does not seem to be commonly known; for it has been collected to the amount of several pounds weight, as being merely sand, without any other particles of stone.[11]
“The magnet-iron displays also, in several places, brittle iron-ore, and reminds me of similar occurrences in the large mica-slate mountain-chain of the Brazils.
“We do not possess, unfortunately, any specimens from the high mountains of Enarea, but the stones of the lands of Bertat, Sennaar, and Fazògl, are well known through M. Russegger’s excellent collection. There are granite and gneiss mountains in the land of Bertat, and in the southern part of Fazògl; chlorite slate (probably the stone bringing gold here) follows this chain towards the north, together with mica-slate; and lastly, in Sennaar, there is also clay-slate. In the latter, which is very much changed in some places, veins of granite and quartz are at the top, so that here also, as in many other points, the clay-slate appears the more ancient, the granite the more modern stone. Granite is met with likewise on the Bah’r el Abiad, in the Jebel Njemati (Iemati), being partly of pink feldspar, white albin, grey quartz and black mica, and partly composed without albin, and only of dark red feldspar, white quartz, and black mica.
“Similar species of rocks are found in Kordofàn, viz., granite, gneiss, and mica-slate. However, diorite makes its appearance towards the south, consisting of white feldspar, green and black hornblende, and a little volcanic sand. On the island of Tira there is also chlorite slate. But the most remarkable thing is the appearance of clinkstone or phonolite, found in Koldadschi (written also Kodalgi and Koldagi), in Russegger’s collection.
“This circumstance is conclusive of a considerable development of basaltic stones in these regions, though it does not denote volcanic phenomena; for phonolite, with us, only appears in those basaltic mountain-groups where there has not been any eruption of volcanoes.
“A sandstone and hornstone formation, probably belonging to the latter tertiary rocks, is situated before the mountain-chain of Kordofàn and Sennaar, to which Mount Mandera, which consists of syenite, is united in the east. It forms the Jebel Mussa, specimens from which have been given both by Russegger and Werne.
“We wind up the geognostical picture of these countries by saying that we find granite, gneiss, and mica-slate generally spread, with which clay-slate, chlorite-slate, and diorite present themselves, all of the earlier formation,—new stones of basalt, phonolites, and volcanoes, springing from the tertiary epoch, join on immediately to the others. The limestone conglomerates, found in the Sobàt, have perhaps their origin in chalk lime-stone, to which they belong apparently, judging from external appearances; and if this should be the case, the geognostical relations of the eastern part of central Africa are closely allied to those of Palestine, Syria, and Asia Minor.”
THE END.
London:
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