605 



but without passing to syenite (Vol. v, p. 18, 

 435). Those modifications are observed on 

 the banks of the Oroonoko, the Cassiquiare, the 

 Atabapo, and the Tuamini, The biocks heaped 

 together which are found in Europe on the 

 ridge of granitic mountains (Riesengebirge in 

 Silesia, Ochsenkopf in Franconia), are above 

 all remarkable in the north-west part of the 

 Sierra Parime, between Caycara, the Encara- 

 mada, and Uruana, in the cataracts of the May- 

 pures and at the mouth of the Rio Vichada 

 (Vol. v, p. 177). It remains doubtful if these 

 heaved-up masses, of cylindric form (Vol. iv, 

 p. 540), parallelipedes rounded on the edge, or 

 balls of 40 to 50 feet in diameter (Vol. v, p. 616, 

 &c), are the effect of a slow decomposition, or 

 of a violent and instantaneous heaving-up. The 

 granite of the south-east part of Sierra Parime 

 sometimes passes to pegmatite % composed of 

 larninary feldspar, enclosed in curved masses of 

 crystalline quartz. I saw gneiss only in subor- 

 dinate layers^; but ; between Javita, San Car- 



nite of the chain of the coast of Venezuela, unless at the 

 summit of the Silla de Caraccas (Vol. hi, p. 505). 



* Schrift-granit. It is a simple modification of the com- 

 position and texture of granite, not even a subordinate layer. 

 It must not be confounded with the real pegmatite, gene- 

 rally destitute of mica, or with the geographic stones ( piedras 

 mapajas) of the Oroonoko (Vol. v, p. 559), which contain 

 streaks of dark green mica variously turned. 



+ The magnetic sands of the rivers that furrow the gra- 



