ROCKS OF T1IE PLAIKS. 136 



transition-slates,* and on the south it rests immediately on 

 the granites of the Orinoco. We observed in it rounded 

 fragments of quartz (kieselschiefer), and Lydian stone, 

 cemented by an olive-brown ferruginous clay. The cement 

 is sometimes of so bright a red that the people of the 

 country take it for cinnabar. We met a Capuchin monk at 

 Calabozo, who was in vain attempting to extract mercury 

 from this red sandstone. In the Mosa de Paja this rock con- 

 tains strata of another quartzose sandstone, very fine-grained ; 

 more to the south it contains masses of brown iron, and 

 fragments of petrified trees of the monocotyledonous family, 

 but we did not see in it any shells. The red sandstone, 

 called by the Llaneros, the stone of the reefs (piedra de 

 arrecifes), is everywhere covered with a stratum of clay. 

 This clay, dried and hardened in the sun, splits into separate 

 prismatic pieces with five or six sides. Does it belong to 

 the trap-formation of Parapara ? It becomes thicker, and 

 mixed with sand, as we approach the Bio Apure ; for near 

 Calabozo it is one toise thick, near the mission of Gruayaval 

 five toises, which may lead to the belief that the strata of 

 red sandstone dips towards the south. We gathered in the 

 Mesa de Pavones little nodules of blue iron-ore disseminated 

 in the clay. 



A dense whitish-gray limestone, with a smooth fracture, 

 somewhat analogous to that of Caripe, and consequently 

 to that of Jura, lies on the red sandstone between Tisnao 

 and Calabozo.f In several other places, for instance in the 

 Mesa de San Diego, and between Ortiz and the Mesa de 

 Paja,J we find above the limestone lamellar gypsum alter- 

 nating with strata of marl. Considerable quantities of this 

 gypsum are sent to the city of Caracas, which is situated 

 amidst primitive mountains. 



This gypsum generally forms only small beds, and is 

 mixed with a great deal of fibrous gypsum. Is it of the 



* At Malpaso and Piedras Azules. 



f Does this formation of secondary limestone of the Llanos contain 

 galena ? It has been found in strata of black marl, at Barbacoa, between 

 Tmxillo and Barquesimeto, north-west of the Llanos. 



J Also near Cachipe and San Joacquim, in the Llanos of Barcelona. 



This trade is carried on at Parapara. A load of eight arrobas sell* at 

 Caracas for twenty* four piastres. 



