122 O. W. Bubnan — The Geological Chronometer. 



VI. — The Geological Chronometer. 

 By G. W. BuLMAN, Esq. 



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 tliere, 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, 

 080,000,000. In other words, the greatest rate of foi-mation is more 

 than nine times the least. We ought, then, to be able to put the 

 question to the test of actual observation. Do the deposits formed 

 at the greater rate differ in any essential characters from those 

 formed at the lesser? If we can establish any difference by 

 observing recent deposits, then we can apply the criterion to the 

 strata of past ages. But, so far as I am aware, no geologist has 

 pointed out any specific characters by which a quickly formed 

 deposit can be certainly distinguished from a slowly formed one. 

 This may be, of course, that they have not specially looked for 

 such characters. It seems more probable, however, that there are 

 no reliable criteria. 



" The geological agency to which attention is chiefly directed by 

 those who desire to hurry up the phenomena of rock formation," 

 Professor Poulton tells us, " is that of tides." And to prove that 

 tides were not sufficiently high in time past to do so, two things are 

 relied on. 



First, that the rocks indicate deposition under tranquil conditions, 

 and secondly, that "extremely delicate organisms" are found in them. 



" There are, then, among the older Paleeozoic rocks a set of deposits 

 than which we can imagine none better calculated to test the foi'ce 



1 Presidential Address to the Biological Section (D), Brit. Assoc, Liverpool, 1896. 



