Ch. xil] fossil kemains in drift. 137 



Isles of sub-aerial glaciers. Dr. Buckland published in 1842 his reasons foi 

 believing that the Snowdonian mountains in C&ernarvonshire were former- 

 ly covered with gla(?iers, which radiated from the central heights through 

 the seven principal valleys of that chain, where striae and flutings are seen 

 on the polished rocks directed towards as many different points of the 

 compass. He also described the " moraines" of the ancient glaciers, and 

 the rounded " bosses" or small flattened domes of polished rock, such as 

 the action of moving glaciers is known to produce in Switzerland, when 

 gravel, sand, and boulders, underlying the ice, are forced along over a 

 foundation of hard stone. Mr. Darwin, and subsequently Prof. Ramsay, 

 have confirmed Dr. Buckland's views in regard to these Welsh glaciers. 

 Nor indeed was it to be expected that geologists should discover proofs of 

 icebergs having abounded in the area now occupied by the British Isles 

 in the Pleistocene period without sometimes meeting with the signs of 

 contemporaneous glaciers which covered hills even of moderate elevation 

 between the 50th and 60th degrees of latitude. 



In Ireland the " drift" exhibits the same general characters and fossil re- 

 mains as in Scotland and England ; but in the southern part of that island. 

 Prof. E. Forbes and Capt. James found in it some shells which show that 

 the glacial sea communicated with one inhabited by a more southern fauna. 

 Among other species in the south, they mention at Wexford and elsewhere 

 the occurrence oi Nucula Cohholdice (see fig. 125, p. 155) and Tiirritella 

 incrassata (a crag fossil) ; also a southern form of F'usus, and a Mitra 

 allied to a Spanish species.* 



CHAPTER XII. 



Difficulty of interpreting the phenomena of drift before the glacial hypothesis was 

 adopted — Effects of intense cold in augmenting the quantity of alluvium— - 

 Analogy of erratics and scored rocks in North America and Europe — Bayfield 

 on shells in drift of Canada — Great subsidence and re-elevation of land from the 

 sea, required to account for glacial appearances — Why organic remains so rare 

 in northern drift — Mastodon giganteus in United States — Many shells and some 

 quadrupeds survived the glacial cold — Alps an independent centre of dispersion 

 of erratics — Alpine blocks on the Jura — Whether transported by glaciers or 

 floating ice — Recent transportation of erratics from the Andes to Chiloe — Me- 

 teorite in Asiatic drift. 



It will appear from what was said in the last •chapter of the marine 

 shells characterizing the boulder formation, that nine-tenths or more of 

 them belong to species still living. The superficial position of " the drift" 

 is in perfect accordance with its imbedded organic remains, leading us to 

 refer its origin to a modern period. If, then, we encounter so much dif- 

 ficulty in the interpretation of monuments relating to times so near our 

 own — if in spite of their recent date they are involved in so much ob- 

 scurity — the student may ask, not without reasonable alarm, how we can 

 hope to decipher the records of remoter ages. 



* Forbes, Memoirs of Geol. Survey of Great Britain, vol. i. p. oil. 



