On the Vents of Hot Vapor in Tuscany. 201 
lowish, sandy marlstone—in parts a travertine. This band clearly 
overlies the subapennine marls of the adjacent hills and valleys 
on the north, in which the rock salt and springs of Volterra oceur, 
and is probably of the same age as the uppermost yellow marine 
panchina’ of Tuscany, or as the lacustrine deposit in the valley 
of the Elsa, which I have alluded to in a previous memoir.* 
Charged with land and freshwater shells, this rock is disposed in 
horizontal masses, and denuded into abrupt escarpments, which 
in the middle ages formed the natural defences of the old feudal 
rocks of serpentine and gabbro rise up through strata of whitish 
grey alberese limestone and some contiguous schists and sand- 
a line from N. by W. to S. by E. (fig. 1.) The sides of this’ 
valley consist chiefly of alberese limestone and schists, with 
‘Some points of protruding serpentinous rocks, the lower slopes 
being partially covered, as far as observation was possible, with 
4 2 a 
t eter Bos Loud, Tol, bien Firenze, 1846. Estratta defla 
Gazzetta Toseana delle Scienze Medico-fisiche, An. 4, 2 In this memoir bene, 
it iw 
ore oor 
_ Scoxp Serres, Vol, XI, No. 32.—March, 1851. 
