IX GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE Merchants occasionally go through a wholesome, though troublesome and not always satisfactory, process which they term "taking stock."

A geological formation is the sum of all the strata deposited over the whole surface of the earth during one of these epochs: a geological fauna or flora is the sum of all the species of animals or plants which occupied the whole surface of the globe, during one of these epochs.

These assumptions are two: the first, that the commencement of the geological record is coëval with the commencement of life on the globe; the second, that geological contemporaneity is the same thing as chronological synchrony.

of species of Mollusca in common, and comparatively close together, may yet be separated by an amount of geological time sufficient to allow of some of the greatest physical changes the world has seen, what becomes of that sort of contemporaneity the sole evidence of which is a similarity of facies, or the identity of half a dozen species, or of a good many genera?

And yet there is no better evidence for the contemporaneity assumed by all who adopt the hypothesis of universal faunae and florae, of a universally uniform climate, and of a sensible cooling of the globe during geological time.

Are all the grandest and most interesting problems which offer themselves to the geological student, essentially insoluble?

But, pending the construction of a surer foundation than palaeontology now possesses, it may be instructive, assuming for the nonce the general correctness of the ordinary hypothesis of geological contemporaneity, to consider whether the deductions which are ordinarily drawn from the whole body of palaeontological facts are justifiable.

We are all accustomed to speak of the number and the extent of the changes in the living population of the globe during geological time as something enormous: and indeed they are so, if we regard only the negative differences which separate the older rocks from the more modern, and if we look upon specific and generic changes as great changes, which from one point of view, they truly are.

[Footnote 5: "Memoirs of the Geological Survey of the United Kingdom.

The PROTOZOA.The Protozoa are represented throughout the whole range of geological series, from the Lower Silurian formation to the present day.

In these groups there is abundant evidence of variationnone of what is ordinarily understood as progression; and, if the known geological record is to be regarded as even any considerable fragment of the whole, it is inconceivable that any theory of a necessarily progressive development can stand, for the numerous orders and families cited afford no trace of such a process.

By Sir W. Thomson, LL.D. Transactions of the Geological Society of Glasgow, vol.

By CATASTROPHISM, I mean any form of geological speculation which, in order to account for the phenomena of geology, supposes the operation of forces different in their nature, or immeasurably different in power, from those which we at present see in action in the universe.

Nor can it be questioned that Uniformitarianism has even a stronger title than Catastrophism to call itself the geological speculation of Britain, or, if you will, British popular geology.

This subject is usually left to the astronomer; but a knowledge of its broad outlines seems to me to be an essential constituent of the stock of geological ideas.

The sort of geological speculation to which I am now referring (geological aetiology, in short) was created, as a science, by that famous philosopher Immanuel Kant, when, in 1775, he wrote his "General Natural History and Theory of the Celestial Bodies; or an Attempt to account for the Constitutional and the Mechanical Origin of the Universe upon Newtonian principles.

He knows no bounds to geological speculation but those of the intellect.

Such being the three phases of geological speculation, we are now in position to inquire which of these it is that Sir William Thomson calls upon us to reform in the passages which I have cited.

It is obviously Uniformitarianism which the distinguished physicist takes to be the representative of geological speculation in general.

And thus a first issue is raised, inasmuch as many persons (and those not the least thoughtful among the younger geologists) do not accept strict Uniformitarianism as the final form of geological speculation.

Sir William Thomson believes that he is able to prove, by physical reasonings, "that the existing state of things on the earth, life on the earthall geological history showing continuity of lifemust be limited within some such period of time as one hundred million years" (loc. cit.

If the geological clock is wrong, all the naturalist will have to do is to modify his notions of the rapidity of change accordingly.

But if, on the other hand, the 100,000,000 or 200,000,000 years appear to be insufficient for geological purposes, we must closely criticise the method by which the limit is reached.

It is now no part of recognised geological doctrine that the species of one formation all died out and were replaced by a brand-new set in the next formation.

But that we should do so no more follows than that we should envy those geological ages when the club-mosses were of the size of forest-trees, and the frogs as big as oxen.