changed tlie Surface of Switzerland. 31 



When these fragments are larger it becomes the gompliolite of 

 Brongniart, and the Nagelfluh of the Germans. Owing to the 

 size of the fragments, in this instance, their form and nature are 

 easily recognisable. We find that they are rubbed and rounded 

 exactly like the pebbles of our rivers,* that a great number of 

 them belong to rocks which are found in situ in our Alps ; but 

 that there are also many which have been derived from rocks 

 that would be sought for in vain throughout Switzerland. 



This remarkable fact, joined to the arrangement of those con- 

 glomerates which are generally found situated at the foot of the 

 Alps, and which only assume the form of Molasse when removed 

 to a certain distance from them, renders it probable that all those 

 materials were furnished by the first soutivement of the Alps 

 themselves. They would in that case be the debris of the rocks 

 which, during that terrible catastrophe, were fractured, broken, 

 rubbed, and triturated in a thousand different ways. Several of 

 them must have been torn from great depths, and from rocks 

 which our valleys have not reached, and which consequently our 

 Alps have not exposed. 



Beds of lignite (a species of coal) accompanied by remains of 

 molluscous fresh water animals, and even by some species of 

 Mammalia, shew, by their presence in the interior of the Mo- 

 lasse, that during the epoch of the formation of the latter, the 

 sea retired several times and left this formation dry ; and this 

 for a length of time sufficient to permit the formation of fresh 

 water marshes, the establishment of vegetation on them, and 

 an order of things fit for the creation of terrestrial animals. It 

 is impossible to determine whether these retirings of the sea took 

 place in consequence of a lowering of its level, or, as appears 

 more probable to us, were owing to a slight momentary souleve- 

 rnent of the formation, which, sinking down afterwards, was again 

 submerged. 



During the epoch of the formation of the Molasse, the por- 

 tion of Switzerland in which our canton is included formed 

 part of a vast island. This country was bounded on the north 

 and north-west by the southern chain of the Jura ; and on the 



* M. Studer, in his classical work on the Molasse, has perfectly explained 

 the cause of the difference of form in the large and small fragments. 



