It should not be forgotten, however, that from one point of view there is a truth in catastrophism which is sometimes overlooked by the advocates of continuity and uniformity.  Catastrophism has, as its essential feature, the proposition that the known and existing forces of the earth at one time acted with much greater intensity and violence than they do at present, and they carry down the period of this excessive action to the commencement of the present terrestrial order.  The Uniformitarians, in effect, deny this proposition, at any rate as regards any period of the earth’s history of which we have actual cognisance.  If, however, the “nebular hypothesis” of the origin of the universe be well founded—­as is generally admitted—­then, beyond question, the earth is a gradually cooling body, which has at one time been very much hotter than it is at present.  There has been a time, therefore, in which the igneous forces of the earth, to which we owe the phenomena of earthquakes and volcanoes, must have been far more intensely active than we can conceive of from anything that we can see at the present day.  By the same hypothesis, the sun is a cooling body, and must at one time have possessed a much higher temperature than it has at present.  But increased heat of the sun would seriously alter the existing conditions affecting the evaporation and precipitation of moisture on our earth; and hence the aqueous forces may also have acted at one time more powerfully than they do now.  The fundamental principle of catastrophism is, therefore, not wholly vicious; and we have reason to think that there must have been periods—­very remote, it is true, and perhaps unrecorded in the history of the earth—­in which the known physical forces may have acted with an intensity much greater than direct observation would lead us to imagine.  And this may be believed, altogether irrespective of those great secular changes by which hot or cold epochs are produced, and which can hardly be called “catastrophistic,” as they are produced gradually, and are liable to recur at definite intervals.

Admitting, then, that there is a truth at the bottom of the once current doctrines of catastrophism, still it remains certain that the history of the earth has been one of law in all past time, as it is now.  Nor need we shrink back affrighted at the vastness of the conception—­the vaster for its very vagueness—­that we are thus compelled to form as to the duration of geological time.  As we grope our way backward through the dark labyrinth of the ages, epoch succeeds to epoch, and period to period, each looming more gigantic in its outlines and more shadowy in its features, as it rises, dimly revealed, from the mist and vapour of an older and ever-older past.  It is useless to add century to century or millennium to millennium.  When we pass a certain boundary-line, which, after all, is reached very soon, figures cease to convey to our finite faculties any real notion of the periods