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This change in the geological configuration of the shore extends far beyond the mouth of the Apure. We had begun to observe it in this latter river as far off as Algodonal and the Cano del Manati. The spangles of mica come, no doubt, from the granite mountains of Curiquima and Encaramada; since further north-east we find only quartzose sand, sandstone, compact limestone, and gypsum.
A red, quartzose, fine-grained conglomerate, with grains of quartz, and with patches of white earthy feldspar, apparently due to some process of concretionary crystalline action; this bed is more compact and metamorphosed than any of the overlying conglomerates. 5th. A whitish cherty limestone, with nodules of bluish argillaceous limestone. 6th.
Below this are Lower Miocene strata about 300 feet in thickness, in the upper part of which are twenty-six beds of lignite, clay, and sand, and at their base a ferruginous quartzose sand, varying in thickness from two to twenty-seven feet. Below this sand are forty-five beds of alternating lignite and clay.
The quartz predominates in the mass; and is generally of a milky white. I observed neither hornblende, black schorl, nor rutile titanite, in this granite. In some ledges we recognised round masses, of a blackish gray, very quartzose, and almost destitute of mica. They are from one to two inches diameter; and are found in every zone, in all granite mountains.
Far beyond its right bank rose an Ash'hab, or "grey head," which seemed to promise quartzose granite: it will prove an important feature. Before sleeping, I despatched to El-Wijh two boxes of micaceous schist and two bags of quartz, loads for a pair of camels.
Cambrian conglomerate and sandstone. 3, 3'. Quartzose Lower Silurian, with annelid burrows. 3a. Fossiliferous Silurian limestone. 3b.
Next in the descending order are the shales and sandstones in which the quartzose rocks called Stiper-Stones in Shropshire occur. I have seen similar burrows now made on the retiring of the tides in the sands of the Bristol Channel, near Minehead, by lob-worms which are dug out by fishermen and used as bait.
The waters, which are loaded with sulphuretted hydrogen, issue from a quartzose sandstone, lying on compact limestone, the same as that we had examined at the Morro. We again found in this limestone intercalated beds of black hornstein, passing into kieselschiefer. The real kieselschiefer and Lydian-stone have not been observed hitherto except in the transition-slates and limestones.
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