th-east slopes of the Sierra de Cochabamba a
little south of the 17th parallel, and follows a northerly serpentine
course to its confluence with the Beni, the greater part of which course
is between the 65th and 66th meridians. The river has a length of about
600 m., fully three-fourths of which, from Chimore (925 ft. above sea
level) to the rapids near its mouth, passes across a level plain and is
navigable. The principal Bolivian tributary of the Mamore, the Guapay or
Grande, which is larger and longer than the former above their
confluence and should be considered the main stream, rises in the
Cordillera Oriental east of Lake Pampa Aullaguas, and flows east to the
north extremity of the Sierra de Misiones, where it emerges upon the
Bolivian lowlands. Turning to the north in a magnificent curve, it
passes around the south-east extremity of the Sierra de Cochabamba,
skirts the Llanos de Chiquitos, and, turning to the north-west, unites
with the Mamore at Junta de los Rios in about 15 deg. 20' S. lat. and 64
deg. 40' W. long. It has a tortuous course of over 700 m., which is
described as not navigable. The principal tributaries of the Guapay are
the Mizque, Piray or Sara and Yapacani, the last rising on the east
slopes of the Cordillera Real, flowing east by Cochabamba to the
sierras of that name where it breaks through with a great bend to the
north. The other large Bolivian tributaries of the Mamore, all rising on
the north-east flanks of the Andes, are the Chapare, Secure, Manique or
Apere and Yacuma, the last draining a region of lakes and swamps north
of the Sierra Chamaya. The Beni and its great affluent, the Madre de
Dios, though of smaller volume and extent than the Mamore, are of much
greater economic importance, owing to their navigability, the fertility
of the region they drain, and the great forests along their banks. North
of the Beni, the Abuna flows into the Madeira. Several of its south
tributaries belong to Bolivia. The Guapore, or Itenez, an affluent of
the Mamore, is the third large river of this Bolivian drainage basin,
but it rises in Brazil, on the south slopes of the Sierra dos Parecis,
where it flows in a great bend to the south and then west of north to
the Bolivian frontier in 14 deg. S. lat. From this point to its junction
with the Mamore, a little north of the 12th parallel, it flows in a
northwesterly direction and forms the boundary line between the two
republics. Its Brazilian tributaries ar