342 APPENDIX. Xo. XV. 



These terraces were doubtless formerly much more continuous 

 than at present, later denudation having destroyed portions of 

 them ; but the numerous fragments that remain, preserved 

 by a protective snow mantle, are sufficient to show that they 

 were formed by the processes now in progress of operation. 



The mud and sand-beds formed during the earlier stage 

 of upheaval are carried down by summer torrents, and dis- 

 charged into fiords and arms of the sea ; the heated and turbid 

 waters melting the floes lying around the delta, and causing 

 it to discharge its freight of stones and gravel into the mud- 

 beds beneath, into which also fall the shells of the mollusca 

 inhabiting the coast. These mud-beds on the upheaval of 

 the country are covered by stream-action with unfossiliferous 

 gravels, which, together with the mud-beds, often form a 

 thickness in the valleys of 200 or 300 feet. 



The sequence of formation is constantly repeated as the 

 rise of the land gradually goes on ; the turbid matter in the 

 summer torrent is precipitated, the delta increases in thick- 

 ness, until the bay is^ silted up by a bar across it in great 

 measure thrown up by the irresistible pressure of the Polar 

 pack exerted on the floebergs, which buries them deep in the 

 soft material, and thrusts it up into a bar ; and the bay 

 becomes a lake. Upheaval continuing, the waters seek an out- 

 let ; a passage through the barrier is cut, the waters of the lake 

 are lowered, and expanses of mud, strewed with My a truncata, 

 Saxicava rugosa, Asiarte borealis, are exposed. This surface 

 during ten months of the year is frozen as hard as any rock, but 

 during the thaw episode is exposed to extensive denudation, 

 and its materials carried down to lower levels. 



The molluscan fauna, found in the glacio-marine deposits 

 of Grinnell Land and North Greenland at various levels up 

 to 1,000 feet above the present sea-level, is practically identi- 

 cal with that now living in the neighbouring sea, and the 

 species Pecten groenlandicus, Mya truncata, and Saxicava 

 rugosa are alike most abundant in the modern seas, and in 

 the older mud-beds ; and it is especially worthy of note, as 

 indicating the comparatively modern elevation of this coast- 



