i873-] Notices of Books. 257 



In introducing his own explanation, Col. Drayson begins by 

 examining the three principal movements of the earth — its rota- 

 tion on its axis, its revolution round the sun, and especially the 

 slow movement of its axis round the pole of the ecliptic. It is 

 almost universally laid down by astronomical authorities that the 

 pole of the heavens moves in a circle round the pole of the 

 ecliptic, as a centre, constantly maintaining an angular distance 

 of 23 28' from that centre. The author seeks to refute this 

 generally-accepted proposition, and endeavours to prove that the 

 earth's axis describes a circle — not round the pole of the ecliptic 

 as a centre, but round another centre 6° distant from the pole. 

 As the full astronomical discussion of this movement is reserved 

 for a forthcoming volume, we withhold criticism on this part of 

 the work, and confine ourselves to the geological consequences 

 which tend to flow from the author's data. 



Assuming Col. Drayson's premisses, it follows that during one 

 revolution of the pole of the heavens round the pole of the 

 ecliptic, occupying about 31,840 years, there must be a variation 

 of 12 in the obliquity of the ecliptic. This variation is sufficient 

 to account for extraordinary changes of climate on the surface of 

 the earth. It is calculated that at the date 13,702 B.C. the obli- 

 quity was at its maximum, namely, 35 25' 47". At that time, 

 therefore, the arctic circle would be brought down to this distance 

 from the pole, and our own islands would consequently come 

 within the frigid zone. But whilst our winters were thus cha- 

 racterised by arctic severity, the author argues that the summers 

 must have been almost tropical. In winter, then, the country 

 would be covered with a complete mantle of ice, and in summer 

 this would be rapidly thawed, giving rise to heavy floods and 

 vast numbers of icebergs. 



We have seen that, according to our author, the Glacial Epoch 

 was at its height in 13,700 b.c He believes, however, that the 

 occurrence of great alternations of temperature, producing 

 marked effects on the climate, extended over a period of about 

 16,000 years — 8000 before and 8000 after the maximum. The 

 glacial period would, therefore, have begun in 21,700 b.c, and 

 terminated in 5700 B.C. 



Assuming the course of the pole to be uniform, there would 

 be a recurrence of glacial periods every 31,000 years. Prof. 

 Ramsay, from the study of certain beds of breccia, long ago in- 

 sisted on the necessity of recognising earlier glacial periods ; and 

 the very phrasing of Col. Drayson's title, " The Last Glacial 

 Epoch," shows that he, too, believes in previous periods of alike 

 character. Few geologists will, however, agree with the author 

 in his curious suggestion that these extreme climatic conditions 

 may account for the alternation of different beds in our coal- 

 measures, much less for the bands of flint in our chalk. 



In closing Col. Drayson's work, the geological reader, though 

 anxious to accept many of his conclusions, will feel that he must 



