944 The American Naturalist. [October, 
graphical features of Honduras is nevertheless in operation, perhaps 
not noticed in the short time of days, but the more strikingly in the 
long periods of geological ages. 
hese alterations of the form of mountains and valleys we may 
mainly attribute to meteoric agency, in particular to rainfalls, and to 
the lithological character of a great portion of the material of which the 
Hondurian mountains are composed. The rocks on the Pacific slope 
consist principally of rhyolite, andesite, volcanic, tufas, and augitic 
lavas, most of which are not apt to resist the erosive and destroying 
action of water and air, not only on account of friable structure, but of 
the want of stability in their chemical constituents. We see those 
mineral aggregations undergo metamorphic alterations, and thus we 
have, instead of the original finely crystalized hard material, accumu- 
lations of soft tufas, or common clay. A material thus altered can- 
not preserve its original outlines, and cannot resist the ponderous 
waves of water sweeping during the rainy seasons from the heights 
of the interior towards the level of the oceans. 
There are no other meteorological records in existence which might 
inform us of former and ancient events in Honduras, but those which 
were registered by nature herself in form of striking alterations, to 
which the early topographical aspect of that country has been sub- 
jected during a series of epochs up to the present time. 
The changes in the topography of Honduras, and principally those 
produced since the elapse of the tertiary period, as already mentioned, 
are caused by heavy falls of rain, the erosive action of which the 
half-decomposed rock-material could not resist ; it became detached 
and stored away in the depths of the valleys or on the levels of the 
sea-shores, thus producing, after the long periods of geological ages, 
material alterations and changes on the surface, 
At the present time the amount of water in the rivers is in direct 
proportion to rainfalls, and without much doubt has been always de- 
pending upon this phenomenon. We are, therefore, justified in calling 
those huge mineral accumulations of the diluvial and alluvial age, 
on the coastlands or in the interior, direct data and records in regard 
to the quantity of former rainfalls. In order to receive an adequate 
idea of the quantity of debris already used by nature for her process of 
building new plains, let us examine some features of the erosive action 
of water on the mountains themselves. 
We traverse the plain between La Brea and Gnoscoran, and on en- 
tering the latter village we come upon tertiary grounds. A series of 
isolated volcanic mountains rise before us. Some are of the shape of a 
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