ioo Mr. H. H. Howorth on 



and also see its atmospheric effects. Among other things 

 which it contains are two white polar caps. These were 

 observed by Herschell to shrink and enlarge with the- 

 seasons, and there can be little or no doubt that they 

 represent the ice at either pole of Mars. Now, in addi- 

 tion to its physical resemblance to the earth, Mars 

 fulfils the conditions demanded by Dr. Croll, namely, 

 its orbit shows great obliquity, yet nothing is more certain 

 than that the results suggested by Dr. Croll are not forth- 

 coming. We have not one pole with a gigantic icecap, and 

 the other denuded of ice, but both poles have a more or less 

 similar covering, and more or less of the same size, showing 

 coincident and not alternate conditions of extreme cold at 

 each pole. 



This being the recent and contemporaneous evidence 

 furnished by the two hemispheres as to alternate glaciation, 

 what do the older beds have to say in regard to an alterna- 

 tion of cold and warm periods ? 



Let us remember what kind of evidence we ought to 

 have if we are to believe in a recurrence of such conditions 

 as are evidenced by the drift phenomena. As I have already 

 said these phenomena need no microscope to discover them. 

 They are among the most stupendous and the most 

 cosmopolitan monuments furnished by geology. Within 

 the geographical limits of the drift phenomena we can hardly 

 examine a rood of ground without finding traces of them 

 either in the striated boulders, scratched rocks, clays, muds, 

 or in the animal remains. They are present everywhere, 

 and most of them are among the most indestructible of 

 witnesses. Where can we find at any geological horizon 

 facts to parallel these ? The earth has been diligently 

 searched for them, but with the exception of a few uncertain 

 and sporadic and dubious cases of the occurrence of some 

 boulders in old conglomerates, which are compatible with 

 other explanations, where are we to look for evidence ? What 



