Sierra, a chain of mountains between Venezuela and Brazil, extends in a S.W. direction from the western extremity of the Sierra Pacaraima, between N. Lat. 4. and 6.30., W. Long. 64. and 67. They seldom rise higher than 1800 or 2000 feet from the sea; and many of the summits are only 500 or 600 feet in height. In geological structure, the base of the mountains is believed to be of granite, while trap and quartz rocks are also met with. Many of them are bare and rocky, or covered only with grass. The rivers Orinoco and Parima take their origin in this range; the latter flowing first E., then S., and falling into the Rio Negro, an affluent of the Amazon.