t from it resulted
these periodic convulsions. In this theory we see:--first, that the
previously-recognized agency of water was conceived to act, not as by
Werner, after a manner of which we have no experience, but after a
manner daily displayed to us; and secondly, that the igneous agency,
before considered only as originating special formations, was recognized
as a universal agency, but assumed to act in an unproved way. Werner's
sole process Hutton developed from the catastrophic and inexplicable
into the uniform and explicable; while that antagonistic second process,
of which he first adequately estimated the importance, was regarded by
him as a catastrophic one, and was not assimilated to known
processes--not explained. We have here to note, however, that the facts
collected and provisionally arranged in conformity with Werner's theory,
served, after a time, to establish Hutton's more rational theory--in so
far, at least, as aqueous formations are concerned; while the doctrine
of periodic subterranean convulsions, crudely as it was conceived by
Hutton, was a temporary generalization needful as a step towards the
theory of igneous action.

Since Hutton's time, the development of geological thought has gone
still further in the same direction. These early sweeping doctrines have
received additional qualifications. It has been discovered that more
numerous and more heterogeneous agencies have been at work, than was at
first believed. The conception of igneous action has been rationalized,
as the conception of aqueous action had previously been. The gratuitous
assumption that vast elevations suddenly occurred after long intervals
of quiescence, has grown into the consistent theory, that islands and
continents are the accumulated results of successive small upheavals,
like those experienced in ordinary earthquakes. To speak more
specifically, we find, in the first place, that instead of assuming the
denudation produced by rain and rivers to be the sole means of wearing
down lands and producing their irregularities of surface, geologists now
see that denudation is only a part-cause of such irregularities; and
further, that the new strata deposited at the bottom of the sea, are not
the products of river-sediment solely, but are in part due to the
actions of waves and tidal currents on the coasts. In the second place,
we find that Hutton's conception of upheaval by subterranean forces, has
not only been modified by assimi