516 Geological Society. 



and lakes formed upon and within the glaciers. He also investi- 

 gates the action of modern glaciers in polishing and producing striae, 

 ridges and furrows, and rounded bosses resembling wool-sacks 

 (^Roches mouto?mes of De Saussure and Roches bosselees of Hugi), on 

 the surface of the hardest rocks over which they pass ; and also in 

 grinding to the state of pebbles fragments of rocks that are forced 

 along their bottoms, and in transporting to great distances large 

 blocks of stone interspersed through the substance and poised upon 

 the surface of morains. 



Within the records of history the lower terminations of many gla- 

 ciers have varied considerably, and the morains left by them in the 

 valleys show the extent to which the ice has descended in times 

 comparatively modern. Agassiz has recognized the association of 

 similar residuary phsenomena not only in valleys of the Alps below 

 the level of the present glaciers, but along the whole south-east 

 flank of the mountains of the Jura, which run parallel to the Alps at 

 the distance of fifty miles on the north-west side of the great valley 

 of Switzerland. He finds on the Jura limestone, at various heights, 

 from the level of the Lake of Neufchatel to three thousand feet, evi- 

 dences from which he infers that glaciers descending the great 

 valleys of the Alps have extended across the entire valley of Swit- 

 zerland over the lakes of Neufchatel and Geneva (then converted 

 into ice), until their course was stopped and deflected in directions 

 parallel to the Jura by the obstructing barrier which this mountain- 

 chain presented. These evidences consist, 1st, in erratic angular 

 blocks of the granite of Mont Blanc, and other rocks from the high 

 Alps, lodged on the south-east face of the Jura in insulated positions, 

 and frequently upon banks of sand and gravel analogous to the mo- 

 rains now forming in the Alps ; 2ndly, in the frequent occurrence of 

 polished surfaces, striae and furrows on the Jura limestone, similar to 

 those now produced at the bottom of existing glaciers ; Srdly, in the 

 coincidence of these striae with the direction in which a glacier from 

 the Alps would have been deflected by the barrier presented to it 

 by the Jura, and their non-coincidence with the slope of these moun- 

 tains ; 4thly, in the existence upon the polished surfaces of the Jura 

 limestone of funnel-shaped cavities (couloirs)- and small indentations 

 similar to the lapiaz we see daily forming at the bottom of glaciers 

 by small and temporary cascades descending through cracks and 

 chasms of the ice. 



M. Agassiz contends, that this quadruple series of phsenomena, 

 which are common to the south-east slopes of the Jura, and to the 

 bottom of existing glaciers in the Alps, is inexplicable on any 

 theory of aqueous action apart from ice ; and still further argues 

 that the concurrent appearance of similar phaenomena in other re- 

 gions of the world justifies the inference that these also have been 

 the site of glaciers. He moreover infers, that very large portions of 

 the now temperate regions of the globe have for a long period been 

 enveloped with a winding-sheet of snow and ice. 



In November 1840, the evidence of the existence of glaciers in 

 Scotland and the north of England has been brought before us in 



