230 Dr. Gwyn Jeffreys on Arctic 



(August 1877), a list of the recent or living Mollusca brought 

 home by Capt. Feilden and Mr. Hart, the Naturalists of the 

 last of our Arctic voyages ; and I propose to supplement that 

 list with a notice of the Post-tertiary fossils collected not only 

 by the Naturalists, but also by Lieut. Egerton and Dr. Moss, 

 two of the officers of H.M.S. ' Alert.' 



I cannot help sharing Mr. Smith's expression of disap- 

 pointment with the conch ological results of the Expedition. 

 The number of Post-tertiary as well as of recent species of 

 Mollusca is very scanty. In analogous or apparently similar 

 cases of so-called " glacial " and raised sea-beds in Great 

 Britain, Scandinavia, and Canada, which I have examined, 

 I collected in two or three hours a greater number of fossil 

 species than those procured in the Expedition. However, great 

 allowance must be made for the difficult circumstances under 

 which the specimens were collected in such very high latitudes ; 

 and I have no doubt that the Naturalists did their best. The 

 fossil specimens brought home by the Naturalists are in the 

 Museum of Economic Geology, under the charge of the 

 Palaeontologist, Mr. Etheridge, and in the British Museum ; 

 Lieut. Egerton presented his specimens to the Geological 

 Society ; and Dr. Moss kindly placed his at my disposal. 



The subject of the present communication is especially inter- 

 esting to geologists, because it is closely connected with the 

 history of those former conditions and changes of climate 

 which left so many traces in Europe and North America, in 

 the form of raised beaches and sea-beds. The investigation 

 of the organisms, particularly of the Mollusca, imbedded in 

 those deposits becomes highly important for the study of the 

 Post-tertiary or Quaternary epoch, as well in a geographical 

 as in a hydrographical point of view. 



The extent of oscillation to which the earth's crust in the 

 northern hemisphere has been subjected, during a compara- 

 tively recent period, is remarkably exemplified in the case of 

 Saxicava rugosa. The large arctic form of this species in a 

 fossil state has been dredged between the Hebrides and Faroes, 

 at the depth of 2070 feet (345 fms.) ; the same form is abun- 

 dant on the surface at Montreal ; and it has been found on 

 Moel Tryfaen at the height of 1360 feet : a difference of 3430 

 feet between depression and elevation is thus shown. The 

 usual habitat of S. rugosa is shallow water, although I have 

 a specimen from 1230 fms. or 7380 feet, and fragments from 

 1622 fathoms or 9732 feet. The last-mentioned depth, added 

 to the height of the Moel Tryfaen sea- beach, gives a measure- 

 ment of 11,092 feet, being nearly equal to two thirds of the 

 heiffht of Mont Blanc. 



