m 
GEOLOGY AND GEOGRAPHY 
proves the absence of the muriates, which, as an oceanic de¬ 
position, would be present to its deterioration as a cultivable 
grain land. 
Under these features of the case we may escape the impu¬ 
tation of presumption in assigning to a “ fluviatile” action 
solely, the deposit of the lower alluvial plains of this coast, 
upon the established principle in the formation of deltas as 
stated by Lyell, that where the tides and freshes meet, with a 
preponderance of power rendering the tidal action subordi¬ 
nate, as on this coast during the S. W* monsoon, fine silt 
lands are formed in the estuaries and on the coast line, which 
from the want of tenacity are again subject to destruction by 
tides and currents when these latter are of predominant 
power,—were further proof wanting in support of this view 
of the subject it will be found in the ingredients of the soil 
itselfi which contains silicious and micaceous particles in 
combination with the argillaceous matter; the undoubted 
products derived from the wasting and attrition of the primary 
order of rocks. 
Another destructive feature in the formation of this allu¬ 
vium is to be fonnd in the banks of the river, where the 
deposited soil is-seen in separate layers, varied in thickness, 
it may be presumed, by an excess of rain and consequent 
deposit of one series of seasons above those succeeding:—and 
in color and conformation, by the action of currents and 
freshes in the upper course of the streams in penetrating and 
causing the abrasion of formations previously protected by 
those which have been washed away* 
To the corroding action of carbonic acid, may be attributed 
the cavernous stalactitic and stalagmitic character of the 
mountain limestone formation, rather than to the cause 
assigned in the action of the waves of the sea :—the follow¬ 
ing extract from “ Lyeil’s Principles of Geology” will serve 
to elucidate this point more fully. 
“ The subtraction of many of the elements of rocks by the 
solvent power of carbonic acid, ascending both in a gaseous 
state and mixed with spring water in the crevices of rocks, 
must be one of the most powerful sources of those internal 
changes and rearrangements of particles so often observed in 
strata ot every age. 
It rarely happens except in limestone rocks, that the car¬ 
bonic acid can dissolve all the constituent parts of the mass, 
and tor this reason probably calcareous rocks are almost the 
only ones in which great caverns and long winding possages 
are found ” & 1 6 
