M. Agassiz on Glaciers, Moraine.^, and Erratic Blocks. 375 



posed, and were we even to imagine, contrary to every physical 

 law, that they could have conveyed blocks of granite of the 

 size of 50,000 cubic feet, as is that of Pierre-a-Bot, still they 

 must have had their impetuosity diminished some time, and 

 then the remains must have filled up some of the inequalities. 

 Notwithstanding, there are no blocks to be found between the 

 Alps and the Jura. 



If, according to another hypothesis, the great boulders are 

 conceived to have proceeded more gradually amongst great 

 masses of mud and rubbish, so thick as actually to carry them 

 along, how has it happened that these masses have not extin- 

 guished all the inequalities of Switzerland ? How has it hap- 

 pened that the blocks alone should have been deposited after 

 their arrival on the Jura, and the masses of mud which had been, 

 able to convey them so far, should then have flowed away, so 

 as to leave them in their places ? 



There are still additional considerations which oppose them- 

 selves to the admission of any of these currents. 



The erratic blocks of the Jura every where repose on polish- 

 ed surfaces, all those at least which have not been carried be- 

 yond the crests of our mountains, and which have not fallea 

 to the bottom of our longitudinal valleys, as may be seen, 

 throughout the valley of the Creux du Vent. But they do not 

 repose immediately upon these polished surfaces. Wherever the 

 rounded pebbles which accompany the great blocks have not 

 been removed by subsequent influences, it is remarked that 

 small blocks, in other words pebbles of different sizes, form a 

 bed of some inches, and sometimes even of many feet, upon 

 which the great angular blocks repose. These pebbles are also 

 much rounded, even polished, and are heaped up in such a 

 way that the larger are above the smaller, and that these last 

 often pass below into a fine sand, lying immediately over the 

 polished surfaces. This order of superposition which is con- 

 stant, is opposed to all idea of a transport by currents ; for in 

 this latter case the order of the superposition of the pebbles 

 would have been precisely reversed. The presence of a fine 

 sand at the surface of the polished surfaces, proves, beyond dis- 

 pute, that no powerful cause could have been in operation, and 

 that no important catastrophe could have affected the surface of 



