394 Searles V. Wood, Jun. — The Climate Controversy, 



alternations during that gradual refrigeration which is indicated by 

 the change in the Pliocene mollusca before referred to ; but this 

 objection Mr. Croll would no doubt meet by his contention that the 

 periods of warmth would be necessarily those of emergence, or, 

 more accurately, of a recession of the sea due to the attraction of the 

 Southern ice-cap ; and that it is only the periods of gradually in- 

 creasing refrigerence (which would be those of submergence in 

 Northern Europe, owing to the transfer of the ice-cap to the 

 northern hemisphere) which the Pliocene mollusca would record. 

 The value of this contention our present certain knowledge of 

 Pliocene land deposits renders it difficult to test by reference to 

 facts, that knowledge being almost confined, in the case of Western 

 Europe, to the Cromer Forest-bed, and the lacustrine formations of 

 the Arno valley ; but so far as these cases go, they seem to show no 

 appreciable departure from the kind of climate indicated by the 

 marine deposits of nearly similar age; and afford no support 

 to the idea that they accumulated during intervals of warmer 

 climate. As regards such intervals during the Glacial period itself, 

 Mr. Croll has collected together a number of notices brought for- 

 ward by geologists, which he considers prove his case. Most of 

 these refer to discoveries in Scotland ; but as it appears to me that 

 some of the deposits which are treated by Scotch geologists as 

 Glacial belong to the period which, in reference to English deposits, 

 we are accustomed to call Post- Glacial, during the latter part of 

 which period there occurred, in my opinion, some degree of renewed 

 refrigeration and a partial submergence, it may be convenient to 

 summarize the conclusions to which a study of the English Glacial 

 and Post-Glacial formations has led me ; more particularly as Mr. 

 Croll has connected one of the instances upon which he relies to 

 prove these warm intervals of the Glacial period with my name. 



In the first place, I have long contended that the English Glacial 

 beds, inclusive of the unstratified clays, are of marine origin; and 

 I believe that the gentlemen of the Geological Survey employed in 

 the examination of these beds have mostly come to a similar opinion. 

 We have in England an advantage in possessing the sequence of 

 Glacial formations more complete than they are in Scotland, the 

 earlier members of the series being, according to my view, unrepre- 

 sented in the northern portions of Britain ; and throughout this 

 series, from its commencement, with beds lying in juxtaposition to 

 the Crag, and differing but slightly in their molluscan fauna from the 

 latest members of the Crag series, to its termination in the shelly 

 gravels at high elevations in Lancashire, and at Moel Tryfaen, there 

 is, with one doubtful excej)tion, nothing that J. can discover indi- 

 cative of a cessation either of Glacial climate or of marine conditions. 

 This exception refers to the unconformity that I discover between 

 the Lower and Middle Glacial deposits of East Anglia, which appears 

 to me to be very marked, and to have been connected with the 

 principal excavation of the East Anglian valley-system. Unfortu- 

 nately there is nothing yet found to jorove that this valley excava- 

 tion was the result of a conversion of the Lower Glacial deposits into 



