220 Mr. De la Beche on the Differences 



once considered as characteristic of the rocks commonly called 

 transition. 



After having examined the environs of Nice in the win- 

 ter of 1827 — 1828, I presented an account of the geology of 

 that neighbourhood to the Geological Society, which it ap- 

 pears by their Proceedings was read in November last. In it 

 I described the two great secondary formations that occur near 

 Nice: first, a marly arenaceous limestone, which, though un- 

 like the green-sand mineralogically, is nevertheless the equiva- 

 lent of that formation, and contains its characteristic fossils ; 

 and secondly, a rock which, though it contains both crystal- 

 line dolomite and gypsum, I referred to the Jura limestone, in 

 consequence of its mineralogical structure so closely resem- 

 bling the light-coloured compact limestones of that formation. 

 I also took occasion to insist on the little value that could be at- 

 tached to the presence of either gypsum or dolomite, and cited 

 instances of their appearance in many formations. It apjiears 

 by the Proceedings of the Geological Society as published 

 in the Phil. Mag. and Annals for May last, that Dr. Buck- 

 land has read an Appendix to this memoir, containing an ac- 

 count of his journey by the high road from Nice towards the 

 Col de Tende, in which he considers the inferior Nice lime- 

 stones as his older alpine limestone, a supposed equivalent of 

 the zechstein formation of Germany, in which a modification 

 of limestone named rauchwacke constitutes one of the smaller 

 divisions, and has been considered, erroneously in my opinion, 

 characteristic of it*. This rauchwacke, however, does not oc- 

 cur in the immediate vicinity of Nice ; and as there is no zoo- 

 logical evidence produced, I presume that the presence of the 

 gypsum and dolomite is considered sufficient for referring the 

 inferior Nice limestone to the zechstein. In my opinion there 

 is but one limestone in the immediate vicinity of Nice beneath 

 the green-sand, the almost constant mineralogical appearance 

 of which is light-coloured and compact; it contains the gyp- 

 sum, as is seen not far N. from the Col de Villefranche, and 

 the dolomite is mixed with it in all ways, even the same range 

 of beds appealing dolomitic in one place and limestone in an- 

 other. It would appear therefore that Dr. Buckland's objec- 

 tion rests upon its mixture with the gypsum and dolomite. 



* That it is by no means safe to judge of the relative ages of rocks by 

 this niodification of limestone, a formation near La Spezia is no bad ex- 

 ample. The most modern rock in the whole gulf, apparently tertiary, 

 is a fair mineralogical rauchwacke, sometimes occurring as the cement to a 

 conglomerate of pieces of all the rocks in the vicinity, such as is not un- 

 common on the shores of the Mediterranean, and sometimes in a few beds 

 by itself. 



That 



