184 Mr. De la Beche on the Geologi/ of the 



the rolled pebbles of the tertiary conglomerates. Greenstone rocks^ &c. occur 

 abundantly in the mountains of St. Tropez, and at the Estrelles the black 

 trap rocks intersect the red quartzose porphyries, as, according to M. Von 

 Buch they do in the Tyrol. 



The highly inclined position, and the frequent and violent contortions of 

 the dolomite and its accompaniments near Nice, and of the green-sand for- 

 mation by which it is covered, connect these rocks still more closely with the 

 Tyrolese and those of Switzerland. I agree with M. Von Buch in ascribing 

 these phaenomena to the upheaving of the Alps by igneous rocks. The pre- 

 sence of dolomite and even gypsum is, taken singly, characteristic of no for- 

 mation. Magnesian limestone, if not actually crystalline dolomite, is well known 

 in carboniferous limestone ; both dolomite and gypsum are also well known in 

 the zechstein or Alpine limestone, and crystalline dolomite occurs at Feigen- 

 stein* near Nassareith. Dolomite and gypsum are met with in the muschel- 

 kalk of Toulon f ; and the lower parts of that rock are magnesian also in the 

 Vosges ;j;. Dolomite and gypsum occur in the lias or lower members of the oolite 

 beds in the south-west of France§; there is no reason, therefore, why the 

 occurrence of these substances in the neighbourhood of Nice, should make it 

 at all improbable that the formation to which they belong is, as I have repre- 

 sented, the Jura or oolite formation. 



There appears to be not unfrequently an intimate, and as yet unexplained, 

 affinity between gypsum and dolomite. Some rhombic crystals, which M. 

 Verany discovered in great abundance in the gypsum at Sospello, M. Cordier, 

 to whom I gave them for examination, reports to be carbonate of magnesia 

 or dolomite, which, he adds, is found under another form in the gypsum of 

 the Tyrol. On the other hand, rocks which contain magnesian strata often 

 afford gypsum — as the zechstein, the new red sandstone, the muschelkalk, 

 the keuper, and the Jura beds. 



In a former communication to the Society, I pointed out the marked 

 changes which rocks sometimes undergo within the range of a few miles. 

 The changes here observed are much greater, as the range is more extensive. 

 Near the extremity of the peninsula of St. Hospice, included among the dolo- 

 mitic, are some beds of common limestone, which contain Encrinites, traces of 

 coral, and particularly a Favosites, to which M. Risso has given the specific 

 title democraticus. These beds, with the dolomite adjacent, he considers the 



* Von Buch: Leltre a M. de Humboldt, p. 16. Plate II. fig. 9. 



t Von Buch. He was the first to notice it. 



J Elie de Beaumont. 



§ Dufrenoy, Ann. des Mines 1827, vol. ii. p. 345. 



