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The Australasian Scientific Magazine. [August i, 1885. 
or arid? wooded or barren? Do the rocky sides correspond with each 
other in their salient and re-entering angles? How far do they extend into 
the bosom of the mountains? How are the subordinate valleys connected 
with the principal one ? But there is another peculiarity of valleys not to be 
lost sight of. There are some which convey to the traveller the impression 
that he is passing though a mountainous or hilly country, so steep, rugged 
and lofty are the hills by which he is surrounded. It is only on reaching their 
summit that he becomes aware that the country through which he has been 
passing is an extensive plain or table-land, intersected by deep chasms and 
valleys, opened out by volcanic action, or cut through the soft soil by the 
constant efforts of the streams by which it is traversed; such valleys 
of excavation as these have been sometimes, not unaptly, called negative 
valleys. 
3. Rivers . — Scarcely less important than that of mountains is the effect 
of rivers in modifying the geographical configuration of a country. From 
their sources in the mountain recesses to their final disemboguing in the 
ocean, their course, their currents, and their shores afford an endless variety 
of remarks and observations. The depth and colour of the water, the rate at 
which it flows, the cataracts it forms, with the rocks over which its waters 
are precipitated, the eddies and currents by which its course is marked, are 
all deserving of notice, as are also the rocks and shoals which obstruct its 
uniform progress, either interfering with its navigation, or, by projecting 
beyond its ordinary banks, throwing back the rushing torrent on the 
opposite shores, thus causing the gradual fall of cliffs by undermining their 
pecarius foundation. Nor in noting the size or extent of rivers should 
we neglect to state how far up they are navigable, for what vessels; and by 
what means ; whether the mouth is constantly free, or whether it is closed 
by a bar, and how much water there is generally over it. Some rivers, 
however, are not only closed by a bar, but, as in the case of Western 
Australia, are, during periods when the water is low, completely masked by 
the sand-hills or dunes which are blown up, forming a continuous bank 
with the hills which skirt the shores, and only when freshets of more than 
ordinary force come down are these sandy barriers overthrown, and the 
rivers are enabled to find an uninterrupted outlet. In other cases the 
effect of beaches thrown up by the constant set of currents in one direction 
is not so absolutely insurmountable, the streams are only partially deflected 
from their proper course, and, instead of flowing into the sea in a continued 
line, are compelled to run for some distance parallel to the coast, until 
the accumulated backwater has acquired sufficient power to overcome the 
diminished resistance of the sea-beach : this, however, more properly 
belongs to the consideration of the coast line. 
But the description of a river will be imperfect, unless we state the 
number and character of streams which fall into it. And here we have to 
consider the angle at which the rivers join each other, whether the direction 
of the main stream is altered or not by the junction, the relative size of two 
confluent streams, and which of them may be said to preserve its former 
course with the smallest deviation. On the true description of these 
details must depend the question as to which of two confluent rivers should 
be considered as the main or parent stream. Rivers are said to be con- 
fluent when both branches are nearly equally deflected from their former 
direction, and that of the united streams may be said to be the resultant of two 
contrary forces. An affluent is a stream which falls into another, called 
the recipient, without changing the direction of the latter, and entirely 
losing its own. 
