le for short distances
only. In both classes navigation is greatly impeded by sandbars at the
mouths of these rivers, while in the districts of periodical rainfall
it is greatly restricted in the dry season. The more important rivers
of the first division, which are described in more detail under the
titles of the Brazilian states through which they flow, are the
following: the Gurupy, Tury-assu, Mearim, Itapicuru and Balsas, in the
state of Maranhao; the Parnahyba and its tributaries in Piauhy;
Jaguaribe in Ceara; and the Apody and Piranhas in Rio Grande do Norte.
Of these the Parnahyba is the most important, having a total length of
about 900 m., broken at intervals by rapids and navigable in sections.
It receives only one important tributary from Maranhao--the Rio das
Balsas, 447 m. long--and five from Piauhy, the Urussuhy-assu,
Gurgueia, Caninde, Poty and Longa. Piauhy is wholly within its
drainage basin, although the river forms the boundary line between
that state and Maranhao throughout its entire length. All the rivers
in this division are influenced by the periodical character of the
rainfall, their navigable channels being greatly shortened in the dry
season (August-January). In Ceara the smaller rivers become dry
channels in the dry season, and in protracted droughts the larger ones
disappear also.

The rivers of the second division are included in a very great
extension of coast and are influenced by wide differences in climate.
Their character is also determined by the distance of the Serra do Mar
from the coast, the more southern rivers having short precipitous
courses. The more northern rivers are subject to periodical variations
in volume caused by wet and dry seasons, but the greater distance of
the coast range and the more gradual breaking down of the plateau
toward the sea, give them longer courses and a greater extent of
navigable water. North of the Sao Francisco the watershed projecting
from the plateau eastward toward Cape St Roque, known as the Serra da
Borborema in Parahyba and Rio Grande do Norte where its direction
becomes north-east, leaves a triangular section of the easterly slope
in which the river courses are short and much broken by rapids. The
rainfall, also, is limited and uncertain. The largest of this group of
small rivers is the Parahyba do Norte, belonging to the state of
Parahyba, whose length is said to be le