Origin of the doctrine of alternate periods of repose and disorder.—­It has been truly observed, that when we arrange the fossiliferous formations in chronological order, they constitute a broken and defective series of monuments:  we pass without any intermediate gradations from systems of strata which are horizontal, to other systems which are highly inclined—­from rocks of peculiar mineral composition to others which have a character wholly distinct—­from one assemblage of organic remains to another, in which frequently nearly all the species, and a large part of the genera, are different.  These violations of continuity are so common as to constitute in most regions the rule rather than the exception, and they have been considered by many geologists as conclusive in favour of sudden revolutions in the inanimate and animate world.  We have already seen that according to the speculations of some writers, there have been in the past history of the planet alternate periods of tranquillity and convulsion, the former enduring for ages, and resembling the state of things now experienced by man, the other brief, transient, and paroxysmal, giving rise to new mountains, seas, and valleys, annihilating one set of organic beings, and ushering in the creation of another.

It will be the object of the present chapter to demonstrate that these theoretical views are not borne out by a fair interpretation of geological monuments.  It is true that in the solid framework of the globe we have a chronological chain of natural records, many links of which are wanting:  but a careful consideration of all the phenomena leads to the opinion that the series was originally defective—­that it has been rendered still more so by time—­that a great part of what remains is inaccessible to man, and even of that fraction which is accessible nine-tenths or more are to this day unexplored.