even and dull fracture ; the surface shining, wrinkled by decomposition. “ To the north and south of the Wells of Mafrass.” 72. The same var iety as the preceding, in the shape of a large conical lump, with uneven and corroded glossy surface, enclosing rounded pieces of the same limestone. From ditto. 73. A similar variety of magnesian limestone, forming a botryoidal group of more or less globular concretions, from upwards of half an inch to half aline in diameter, and intimately grown together with each other. “ Meshroo and El Wahr.” 74. Yellowish limestone, of curved-lamellar structure. “ Forming veins in the basaltic rocks in Agutefa.” 75. Brownish-yellow limestone, in stalagmitical irregular layers. “ On the desert, between Mushroo and El Wahr.” 76. Another fragment, apparently part of a large stalagmitic nodule, in layers on a yellow granular mass of carbonate of lime. From ditto. 7 7 . Greyish-brown and hair-brown fibrous limestone, in tabular pieces; the fibres perpendicular, or in an oblique direction to the horizontal planes, straight or slightly curved. In some specimens, the hair-brown layer is sardonyx and onyx-like, succeeded by a red and a white stratum, the .former generally in the form of a crust, with superficial small acute rhombohedrons of carbonate of lime; in others, the hair-brown layer is traversed by white veins. “ Boundaries of Fezzan and Tuarick country.” 78. Sulphate of barytes; a group of bluish and brownish prismatic crystals, (var. ritr&ie of Hafiy), covered by red marie. 79. Common salt, in white, opaque, granular aggregations, externally stained by ferruginous clay.' “ Road between Hamara and Zuela.” 80. A siline incrustation, of yellowish-white colour, partly solid, in thin tables, partly in poWder, composed of carbonate, muriate, and sulphate of soda. “ Near (Jenna,” 1H 81. Carbonate of soda (trona), thick-fibrous foliated, in crusts of the thickness of one-fourth to one-third of an inch, indistinctly crystallized on the upper surface. “ From the trona lakes in Wady Trona.” 82. The same, studded on the upper surface with small limpid cubical crystals of muriate of soda. From ditto. 83. Carbonate of soda, of yellowish and greenish-grey colour, in -masses with diverging radiated fracture. Kanem ? 84. A rolled piece of nearly compact brown ironstone. “ Upper strata from Aghadem to the southward of El Wahr,” 85. Compact brown ironstone, of dark brown colour; an irregularly tubercular nodule, with surface, particularly that of the old fracturai planes, glossy, the recent fracture exhibiting a dull earthy surface. . “ From plains to the southward of Bonjem.” 86. Compact brown ironstone, of deep chesnut-brown colour, in rounded oblong pieces of from one-half to upwards of an inch in diameter, the whole glossy as if varnished ; fracture even, earthy. From ditto ? 87. Fragment of compact brown ironstone, mixed with much quartzy matter. Wady Kawar and Aghadem. 88. Massive and granular brown ironstone, mixed with much yellow iron ochre and sand. “ In loose masses or crusts, on the top of the ridges between Sockatoo and Kashna, and on the low hills around Sockatoo.” 89- Fragments of clayey brown ironstone with ochrey nodules. “ Wady Shiati hills.” 90. A mass; mixed, of brown ironstone and red and yellow iron ochre. “ From the soil of Wady Sandalion, Tuarick country.” 91. Cubic fragments of common galena, (sulphuret of lead). Kanem, Soudan. 92. Pure tin, cast in moulds, in the form of thick wire. Brought from Soudan. I conclude this long letter with mentioning a specimen of Roman cement, taken from the ruins of Ghirza, which, in parts where the, admixture of small stony fragments is not observable, has very much the appearance of, and might easily be mistaken for, a granular-crystalline variety of tertiary limestone. It has unquestionably undergone a transformation : a circumstance which may, in some measure, serve to justify the remark of Lepère—“ C’est le temps seul et non l’art qui manque à la pétrification absolue de nos mortiers et cimens ; nos neveux diront de nos constructions ce que nous disons de celles, des anciens.” I have the honour to be, my dear Sir, Yours very faithfully, C h a r l e s K o n ig . To Major Denham, &c.
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