SIERRA, a mountain chain of South America, forming the boundary between Venezuela and Brazil. It divides the waters of the Orinoco and Essequibo on the N., from the Amazon and its affluents on the S., and extends E. and W. for about 200 miles, near the 4th degree of N. Lat. The height of the range towards the E. does not exceed 1500 feet; but Mount Pacaraima, near the western extremity, is estimated at 2000 feet high. The geological formation of the mountains is for the most part granite; and they are in general quite destitute of wood, forming a boundary between the dense forests on the N., and the vast grassy savannahs on the S.