270 SCIENCE PROGRESS 



To THE Editor of " Science Progress " 



THE DATE OF THE LAST ICE AGE 



From Major R. A. Marriott, D.S.O. 



Dear Sir, — Before replying to Mr. Tyrrell's letter in the July number of 

 Science Progress, I have something to say about the improved prospect 

 of solving this question geologically. 



It seems that the time has arrived when so much evidence has been 

 collected bearing on the recency of the last glaciation that the question may 

 be now treated primarily on geological lines of evidence, showing that on 

 the geological side alone we are in possession of facts which enable us, quite 

 as much as in any other ordinary geological assumption, to deduce an accep- 

 table scheme of successive cosmical events in late earth-history. 



Adopting the truism that the obliquity of the ecliptic (O.E.) entirely 

 rules the character of the seasons in these higher latitudes, surely, if opinions 

 all over the world, based on the character of rock surfaces, and of morainic 

 and sedimentary deposits, favour the occurrence of a greater obliquity in 

 the near past, while observation records for the last 3,000 years also show a 

 progressive increase in the obliquity, as we go back in time, there is an inherent 

 probability, possessed by no other competing theory, that we are in touch 

 with the real cause of glacial epochs. In addition, it can be shown that 

 astronomical opposition to the acceptance of a marked increase of the O.E, 

 is based on a paradox, which, after being tenaciously held for several genera- 

 tions as a dogma, has become so unsatisfactory that it has had to be now 

 reconstructed by astronomers on the lines of a theory (Drayson's) which 

 dots the i's of geological inferences, and gives a full explanation of the cause 

 of a recent glaciation. Thus, the inherent probability that such geological 

 deductions are sound becomes greatly, and in geometrical ratio, increased. 



With one exception, that of the submerged forests, it is only plain rock- 

 script that has to be read, and yet these forests furnish in themselves sufficient 

 evidence on which to build a working theory of the date and duration of the 

 last glacial period, inasmuch as such evidence explains fully the diagnosis 

 made by Clement Reid as to the date and phases of the forests' submergence. A 

 recognition of this by British geologists is the only link in the chain of a world- 

 wide evidence as to a recent glaciation that is still awaiting authoritative 

 acceptance ; and if judged on the evidence, without prejudice, will be found 

 to fully respond to the requirements of the case, as phenomena which must 

 have accompanied the process of ice accumulation at the poles, and the 

 subsequent process of a steady and continuous refilling of the ocean reservoirs 

 accompanying the final melting of the ice. (See The Submerged Forests and 

 the Last Glaciation, Torquay Nat. Hist. Soc.) 



The controversial underlying astronomical question need not stand in 

 the way of a decision, but may be left to astronomers to work out at their 

 leisure, since geologists can now form their own judgment independently. 

 In pursuance of this method of handling the question, geologists have a further 

 justification from consideration of the following. 



The astronomers say that the cycle of precession lasts about 26,000 

 years ; but it also appears that in the last century or so, during a time of 

 presumably much more accurate observations, the rate of decrease of O.E., 

 as one goes back in time, increases ; and since in the nature of things this in- 

 crease of rate and the before-mentioned increase of the obliquity cannot go on 

 indefinitely, but must change on going back in time to the opposite condition 

 of decrease, to enable the whole cycle to be compassed within 26,000 years, 

 there must be a culminating point beyond which the O.E. cannot go. But 

 whatever this point may have been, from the geological evidence it is clear 



