168 Dr Boue on the Formation of Tertiary Rocks. 



with fresh-water shells, as that of Mayence (p. 170, 174, l85), 

 form the passage between the deposits entirely marine and those 

 of fresh-water formation. 



Notwithstanding he has given in this way all the elements for 

 resolving the problem, M. Brongniart, always thinking of the 

 Paris basin, says, that •' on a cru reconnoitre sous les lignites 

 Suisses d'abord un terrain lacustre plus ou moins epais, et en- 

 suite un terrain de calcaire Parisien,^' — p. 159. These facts, if 

 proved, would indeed decide the question ; but where are the 

 proofs? First, the tritonian limestone is unknown in all the 

 countries of molasse or subapennine clay-marl ; and if a portion 

 of the molasse, that, namely, around the Lake of Geneva, con- 

 tains fresh-water shells, these deposits exist not only near to lig- 

 nite beds, but also in some argillaceous beds, as at Pressy, near 

 Geneva, and Cologny : this being the case, one cannot say, " qu'il 

 n'y a point de coquilles lacustres au milieu meme de la mol- 

 lasse," — p. 148. These shells have been carried by the fluviatile 

 waters, as M. Brongniart acknowledges to have been the case 

 with the palm-tree of Lausanne (p. 148) ; but, from these facts, 

 it does not follow that the molaswse, even in the basin of Geneva, 

 is lacustrine, for the shells are not sufficiently numerous, and 

 are not imbedded in the same way there as in true lacustrine de- 

 posits. These fossils, the lignite as well as the fresh- water and 

 terrestrial shells, which are found so often in the upper tertiary 

 soil of Southern France, of Austria, Hungary, Transylvania, 

 and Gallicia^ or as in some greensand beds, are accidental. 

 Lastly, in considering, in a large marine formation like the mo- 

 lasse, every bed of lignite, or every stratum of fresh-water shells, 

 as lacustrine deposits, we obtain so complex and singular a sup- 

 position, that, even if we had not a more simple and satisfactory 

 opinion to offer, it would fall to be rejected. 



M. Brongniart's idea is entirely founded on his theory of the 

 formation of the deposit of gypsum at Paris. He classes it in 

 the second group of his first division of the lacustrine rocks, viz. 

 that where the mass does not present any sinuous pores (tuhu- 

 lures)^ — a fact so remarkable, that, if true, would change almost 

 entirely the question. He acknowledges that, at the points of 

 contact with the marine deposits, there is an intermixture of 

 fresh-water with marine shells (p. 188) ; but he lays much stress 



