The whole of this vast plain consists of secondary formations which to the southward rest immediately on the granitic mountains of the Orinoco. On the north-west they are separated by a narrow band of transition-rocks from the primitive mountains of the shore of Caracas. This abundance of secondary rocks, covering without interruption a space of more than seven thousand square leagues,* is a phenomenon the more remarkable in that region of the globe, because in the whole of the Sierra da la Parima, between the right bank of the Orinoco and the Rio Negro, there is, as in Scandinavia, a total absence of secondary formations. (* Reckoning only that part of the Llanos which is bounded by the Rio Apure on the south, and by the Sierra Nevada de Merida and the Parima de las Rosas on the west.) The red sandstone, containing some vestiges of fossil wood (of the family of monocotyledons) is seen everywhere in the plains of Calabozo: farther east it is overlaid by calcareous and gypseous rocks which conceal it from the research of the geologist. The marly gypsum, of which we collected specimens near the Carib mission of Cachipo, appeared to me to belong to the same formation as the gypsum of Ortiz. To class it according to the type of European formations I would range it among the gypsums, often muriatiferous, that cover the Alpine limestone or zechstein. Farther north, in the direction of the mission of San Josef de Curataquiche, M. Bonpland picked up in the plain some fine pieces of riband jasper, or Egyptian pebbles. We did not see them in their native place enchased in the rock, and cannot determine whether they belong to a very recent conglomerate or to that limestone which we saw at the Morro of Nueva Barcelona, and which is not transition limestone though it contains beds of schistose jasper (kieselschiefer).