No. XV. GEOLOGY. 



line, that stems of two species of Laminaria, which grow in 

 considerable abundance in the Polar sea, occur in the mud- 

 beds at elevations of 200 feet, still retaining their peculiar 

 sea-shore odour. 



Coniferous wood, still retaining its buoyancy, occurs at ele- 

 vations of several hundred feet, of a precisely similar character 

 to that now being stranded on the existing coast-line. No 

 evidence was discovered in the mud-beds of Grinnell Land to 

 encourage the idea that any of these trees had grown in situ, 

 or that during the period occupied by the elevation of this tract 

 of country a thousand feet, it had experienced an interglacial 

 period during which such trees might have flourished. 



Sea-ice moved up and down by tidal action, or driven on 

 shore by gales, was found to be a very potent agent in the 

 glaciation of rocks and pebbles ; the work was seen in 

 progress along the shores of the Polar Basin, 1 ' at the south 

 end of a small island in BlackclitT Bay, lat. 82 30' N., the 

 bottoms of the hummocks, some eight to fifteen feet thick, 

 were studded with hard limestone pebbles, which when ex- 

 tracted from the ice were found to be rounded and scratched 

 on the exposed surface only.' 



On shelving shores, as the tide recedes, the hummocks, 

 sliding over the subjacent material down to a position of 

 rest, make a well-marked and peculiar sound, resulting from 

 the grating of included pebbles, with the rocky floor beneath, 

 or in some cases on other pebbles included in drift overlying 

 the rock. 



The rock surface at considerable elevations, between gaps 

 in the lines of old terrace, is often found to be glaciated ; and 

 there can be little doubt that this glaciation was produced 

 by shore-ice, during ebbing of the tide, when the land stood 

 lower than at present ; and the condition of the terrace pre- 

 cludes the idea of glacier action. 



The absence of an ice-cap in Grinnell Land, and the 

 paucity of the glaciers in that region, are worthy of note, none 

 descending to the sea-level north of 81 ; while on the same 

 1 Feilden's MSS. Journal. 



