VI.—The Geological Chronometer

Extract

The pleasant relations normally existing among geologists, biologists, and physicists have of late become a trifle strained on the question of the age of the earth. Biologists, having failed to induce either geologists or physicists to draw sufficiently large cheques on the bank of time, have taken to signing the same them-selves, adding the ciphers ad lib. Professor Poulton has ably championed the rights of the biologists to do so, and in the course of his argument he contends that there is evidence in the sedimentary strata to show that their rate of formation was not greater than that at which deposits are now being accumulated.

So far as I am aware, Professor Poulton's contention has not been either controverted or supported by any geologist. Hence it seems to be a suitable subject for discussion in the Geological Magazine.

In the first place, then, what would be the nature of the evidence we might a priori expect to find to show that one set of beds was accumulated in a shorter time than another of equal thickness ? Would there, in fact, be any difference such as would enable us positively to decide the question ?

Secondly, we may examine and compare rocks which we know, or have reason to suppose, have been formed at different rates. Now, according to Sir A. Geikie, if the rocks of the stratified systems were laid down at the greatest rate suggested by the facts of denudation. 73,000,000 years would be required; if at the least, 680,000,000.