258 M. BnoNGNiART onthe &;€. 



It will be seen from this list, that the shelly deposite on 

 the summit of the Montague des Fis contains a great number 

 of shells which almost exclusively belong to the lower chalk 

 (green sand) formation. There are neither belemuites nor 

 terebratulas, because these shells, without being excluded 

 from the green sand (craie chloritee,) are rarely met with 

 in it. 



The shells contained in this deposite so much resemble 

 those of the green sand, that it was sufficient for me to name 

 them. It will also be remarked how much the ammonites 

 differ from those found in the body of the mountain. 



I must confess, that notwithstanding the care I took to 

 procure all the shells of this bed that I could discover at 

 Servoz, among the guides at Chamouni, and at Geneva ; 

 notwithstanding those that have been presented to me by 

 Messrs. Berger, Laine, Soret, Selligue, and Beudant, or 

 that have been sent me by M. Deluc ; I must confess, I say 

 that this list is very incomplete ; but it is sufficiently exten- 

 sive to shew us the proportion in which the green sand shells 

 occur in the Montague des Fis, compared with that of the 

 shells found in the same place, and which have not yet been 

 met with in the green sand. 



These zoological characters and analogies lead us to con- 

 clude that certain rocks of the Perte du Rhone and the 

 summits of the Buet chain should be referred to the green 

 sand formation, notwithstanding the mineralogical dififer- 

 ences at first sight presented by the rocks composing these 

 formations, and those which compose the generally admitted 

 chalk formations. These differences are however greatly 

 diminished by the green grains these rocks contain, and by 

 the greyish and granular rock which covers them, so that 

 the first circumstance, apparently so minute, finishes the 

 analogies I have presented, and offers a new and remarkable 

 application of what I have stated at the commencement of 

 this notice, of the constancy of geological phenomena through- 

 out all the known points of the earth's surface. 



