!30 On the Basaltes of Saxony. 



compact basaltes detached from prisms of the Giant's Cause* 

 wav. hi that of Vicentin, camites have been found. M, de 

 Bcsolding has described an ammonite found in a basaltes of 

 Forez : it still had a pearly splendour. The same naturalist 

 speaks of other ammonites and gryphites contained in ba- 

 saltes in the neighbourhood of Constance. In the last 

 place, there exists in the neighbourhood of Bohemia a large 

 mass of vvacke which contains whole trees half petrified,, 

 and still retaining their bark, and even their leaves. 



This wacke, which envelops whole trees, could not cer- 

 tainly be the production of a volcanic eruption. Basaltes 

 in which shells are found with their pearly splendour does 

 not appear to have been fused. But can these observations, 

 made on some kinds of basaltes, be every where gene- 

 ralized ? If it should result from the state of several of 

 them that they have not an igneous origin, can we thence 

 conclude that all, without exception, are of an aqueous 

 origin ? And does not the existence of certain kinds of 

 basaltes, in places where its position gives reason for classing 

 it among the lava, prove that the crystals in them may, in 

 certain cases, have been subjected to the action of subter- 

 ranean fire without being altered ? 



Here the long discussion which took place on the degree 

 of the heat of volcanoes is renewed. Deluc, Dolomieu, and 

 those who adopt their opinion, will affirm that they saw, as 

 we may say, with their own eyes, torrents of lava the heat 

 of which respected substances much more fusible than horn- 

 blend and feldspar. 



The author of this memoir did not see any of this lava, 

 but he answers this objection by experiments which esta- 

 blish the relative degrees of fusibility of basaltes and of the 

 crystals found inclosed in it. 



The former will set out from their observations to esta- 

 blish the hypothesis of a certain mode of fusion which does 

 not alter the stones subjected to it. 



Their adversaries will insist on experiments and analogies 

 which tend to prove that fused mineral substances exhibit 

 the same phenomena in nature as in our laboratories, and 

 will mention instances of these kinds of lava having burnt, 

 calcined, and destroyed, every tiling they met with in their 

 passage. 



The one, then, will doubt what the others establish as a 

 principle, and will reciprocally inclose each other in a kind 

 of circle, from which it will be difficult for them to escape. 



The question was in this state long before the time when 

 the author of this memoir took it up; and we shall not en- 

 large 



