Searles 7. Wood, Jun. — The Climate Controversy. 397 



its extreme limit, upwards of fourteen million miles nearer to the 

 earth during the winter of the favoured hemisphere than during its 

 summer, so that the seasons would approximate in temperature ; and 

 that then grew the vegetation of the Coal-seams, which is generally 

 admitted to indicate an equable rather than a tropical climate. With 

 these warm periods alternated the cold ones, due to the transference 

 of the perihelion from the winter to the summer, during which the 

 attraction of the ice-cap drew the sea over the coal- growths, which 

 were thus covered by submarine sediment, to emerge again at the 

 return of the perihelion, and form the site of a new growth of 

 vegetation ; and so on successively as the perihelion changed, until 

 the period of high excentricity, giving rise to these alternate con- 

 ditions, passed away. The ingenuity of this hypothesis can hardly 

 be denied ; but if its basis is sound, we ought to find not merely 

 conglomerates and other beds at distant localities occasionally pre- 

 senting features supposed by some to indicate ice-action, but the 

 very Coal-measures themselves which separate the successive Coal- 

 seams in this and other countries, and which are thus referred to 

 intervals of glaciation and submergence, invariably abounding with 

 evidences of ice-action. We have not, however, yet heard of this 

 being the case. Indeed, Mr. Croll, anticipating this objection, 

 endeavours to explain it, on the ground that the Carboniferous land 

 was too low and flat to allow glaciers to form ; and that for the 

 same reason there would be no rocky cliffs to supply boulders for 

 coast-ice to transport and distribute. Considering, however, that the 

 Silurian system had been upheaved and penetrated by eruptive rock 

 before the Carboniferous period, and that yet older rock-masses than 

 the Silurian had been also for ages in existence, and these at no 

 great distance from the Coal-fields of Britain, such an explanation 

 demands larger concessions than most geologists will be willing to 

 grant. 



Finally, in reference to the suggested cause now under considera- 

 tion, it is obvious that if the Glacial period proper was due to 

 the position of the aphelion point, the northern and southern hemi- 

 spheres could not have been synchronously glaciated ; but as the 

 evidence stands at present, this synchronism in glaciation would 

 seem to have been the case. It was a principal object of the expedi- 

 tion made by Louis Agassiz in the year 1872, to examine how far 

 the evidences of former glaciation remaining in the more southern 

 parts of South America lent any support to the theory of alternate 

 glaciations of the two hemispheres ; but he could find nothing in 

 any way leading to the inference that the southern glaciation was 

 not absolutely contemporaneous with the northern ; ^ nor has any- 

 thing, so far as I am aware, been brought forward in reference to the 

 evidences of glaciation furnished by New Zealand that would lead to 

 any different conclusion. Similarly, so far from the features exhi- 

 bited by those formations of very high latitudes in which are 

 preserved the remains of a rich arboreal vegetation lending any 

 support to the theory that the much warmer climate than the 



^ Eeport of the progress of the Hassler Expedition, in Nature for August 1, 1872. 



