358 The Glacial Theory of Prof . Agassiz. 



from Ecluse, near Geneva, to Aarau, a distance of 130 miles. {Sur 

 tout le versant meridional de Jura, depuis le Fort de I'Ecluse jusqu'aux 

 environs d' Aarau.) When the surface is newly exposed, it is smooth 

 as a mirror, marked with furrows and fine scratches, and exhibits the 

 roches moutonnees, or rounded undulations and domes. But the most 

 characteristic fact is, that the furrows do not run from the summit down- 

 ward, hut in a horizontal or ohlique direction, along the face of the 

 ridge, showing that they were impressed by a body moving parallel to 

 the chain along its southern flank. In form and position, they are, in 

 short, precisely similar to the furrows produced by existing glaciers on 

 the sides of the valleys along which they move. Further, these polish- 

 ed and striated rocks are not confined to the declivities of Jura, but are 

 found equally at their foot, in the bottom of the great Swiss valley, 

 wherever the rock is calcareous.* 



In addition to these striated and polished surfaces, Jura has its mo- 

 raines, and in these moraines patches of stratified deposits are found, 

 such as are now formed in small lakes on the flanks of glaciers. It has 

 thousands of erratic blocks, distinctly derived from the Alps ; and, that 

 nothing might be wanting to complete the chain of evidence. Jura has 

 its lapiaz, or water- worn gutters, where no water now runs ; its creux, 

 or water-worn pits, in situations not dominated by any rock whence 

 a cascade could fall ; and its salient peaks, sui'rounded by coronets of 

 boulders, as in figure 7. Now, as no ridge occurs between the Alps 

 and Jura, it is evident that the mass of ice which pressed against the 

 southern declivities of the latter to the height of 3500 feet or more, 

 with a force sufficient to cut and groove the surface longitudinally, 

 must have extended far into the great valley or low country ; and as 

 striated rocks and travelled boulders are also found all over the bottom 

 of that valley, and on the Alps at its opposite side, we have before us 

 a concatenated series of facts, leading almost inevitably to the cenclu- 

 sion that a mer de glace, or vast sheet of ice, once enveloped the Alps 

 and Mount Jura, and covered the whole of the low country between them. 

 Hemmed in by the two mountain chains, the ice could expand only in a 

 northeast or southwest direction, and Agassiz infers from the direction of 

 the stricB, that in the middle and northern part of the valley the motion 

 was northeastwards, or towards the lake of Constance. 



Erratic Blocks of the Alps and Jura. — The large Alpine boulders 

 found on Mount Jura, forty or fifty miles from their native rock, have 

 been a stumbling block to geologists for the last half century. As the 

 subject, though often discussed in books of science, may be new to 

 some individuals, we shall premise a short account of the phenomena. 



* Etudes sur les Glaciers, p. 291. 



