GRANITE AND GNEISS. 379 



I. CO-ORDINATE FORMATIONS or GRANITE, GNEISS, AND 

 MICA-SLATE. There are countries (in France, the vicinity 

 of Lyons; in Germany, Freiberg, Naundorf) where the 

 formations of granite and gneiss are extremely distinct; 

 there are others, on the contrary, where the geologic limits 

 between those formations are slightly marked, and where gra- 

 nite, gneiss, and mica-slate appear to alternate by layers, 

 or pass often from one to the other. These alternations 

 and transitions appeared to me less common in the littoral 

 Cordillera of Venezuela than in the Sierra Parime. We 

 recognise successively, in the former of these two systems 

 of mountains, above all in the chain nearest the coast, as 

 predominating rocks from west to east, granite (long. 

 70 71), gneiss (long. G8 70), and mica-slate (long. 

 65f GG) ; but considering altogether the geologic consti- 



porpliyries issue (like the trachytes of the Andes), in domes from the 

 bosom of inteimediary rocks. Porphyrific breccias, which envelope the 

 quartzose porphyries. (4) Zechstein or Alpine limestone, with marly, 

 bituminous slate, fetid limestone, and variegated gypsum (Productua 

 aculeate), (e) Variegated sandstone (hunter sandstein) with frequent bed* 

 of limestone ; false oolites ; the upper beds are of variegated marl, often 

 muriatiferous (red marl, salzthon), with hydrated gypsum and fetid lime- 

 stone. The gem-salt oscillates from zechstein to muschelkalk. (d) Lime- 

 stone of Gottingen or muschelkalk, alternating towards the top with 

 white sandstone or brittle sandstein. (Ammonitis nodosus, encrinites, 

 Mytilus sociiilis) : clayey marl is found at the two extremities of muschel- 

 kalk. (e) White sandstone, brittle sandstein, alternating with lias, or lime- 

 stone with graphites ; a quantity of dicotyledonous mixed with mono* 

 cotyledonous plants. (/) Jura limestone of complex formation; a quantity 

 of sandy intercalated marl. We most frequently observe, counting from 

 below upwards ; lias (marly lin estone with gryphites), oolites, limestone 

 with polypi, slaty limestone with fish, Crustacea, and globules of oxide of 

 iron (Amonites planulatus, Gryphsea arcuata). (g} Secondary sandstone 

 with lignites ; iron sand ; Wealden clay ; greensand, or green sand- 

 stone ; (A) Chlorite ; tufted and white chalk ; (planerkalk, limestone of 

 Verona.) 



IV. Tertiary strata, showing a much smaller number of dicotyledonous 

 plants, (a) Clay and tertiary sandstone with lignites; plastic clay ; mol- 

 lasse, and nagelfltihe, sometimes alternating, where chalk is wanting, 

 with the last beds of Jura limestone ; amber. (A) Lirnestoi e of Paris or 

 coarse limestone, limestone with circles, limestone of Bolca, limestone of 

 London, sandy limestone of Bognor ; lignites, (c) Silicious limestone, and 

 gypsum with fossil bones alternating with marl, (d) Sandstone of Fon- 

 tainbleau. (e) Lacustrine soil with porous millstone grit, () Alluvial 

 deposits. 



