258 DENUDATION NOT THE ONLY CAUSE OF VALLEYS. 
In strata of higher antiquity, that have been more shattered and 
disturbed by violent convulsions (i. e. in the coal formation, and also 
in transition and primitive rocks), irregularities in the texture and dis¬ 
position of the strata on which the diluvian waters had to exert 
their force have caused the features of the valleys that traverse them 
to be much less exclusively derivative from the simple action of a 
retiring flood of waters; and indeed have rendered the form, in¬ 
clination, hardness, and relative position of the masses on which 
these waters had to operate, essential elements of any accurate 
calculations as to the quantity of effect that must be referred to 
them. Though traces of diluvial action are most unequivocally 
visible over the surface of the whole earth, we must not attribute the 
origin of all valleys exclusively to that action; in such cases as we 
have been describing, the simple force of water, acting in mass on 
the surface of gently inclined and regular strata of chalk and oolite, 
is sufficient for the effects produced ; but in other cases, more espe¬ 
cially in mountain districts, (where the greatest disturbances appear 
generally to have taken place,) the original form in which the strata 
were deposited, the subsequent convulsions to which they have been 
exposed, and the fractures, elevations, and subsidences which have 
affected them, have contributed to produce valleys of various kinds 
on the surface of the earth, before it was submitted to that last 
catastrophe of an universal deluge which has finally modified them 
all. 
