PLIOCENE FORMATION. 173 



the relation of this Crag formation to the Swiss Miocene by the 

 examination of the conditions of stratification. But we have 

 already seen (pp. 91, 92) that, among the marine shells of the 

 Miocene in the Helvetian stage, the living species constitute 

 35 per cent, of the sea-shells, and, further, that in the upper- 

 most or CEningian stage of the Miocene, no true elephants 

 occur, although it possesses two mastodons, which are entirely 

 wanting in the Crag. In the Crag there is another species of 

 mastodon (M. arvernensis) ; and with this true elephants and 

 Hippopotami occur. The English Crag formations are conse- 

 quently younger than the CEningian stage, and occupy the in- 

 terval between it and the lignites. The period of these Crag 

 formations has been called Pliocene, and it is regarded as the 

 third great division of the Tertiary epoch. In the Norfolk 

 forest-bed, and in the Swiss lignites (which maybe denominated 

 the " Utznach formation ") , an indication is afforded of a new 

 period, which has been named the Quaternary or Diluvial 

 period : it is distinguished from the Pliocene by the agree- 

 ment of its flora and marine fauna with those of the present 

 day. 



' A long interval of time manifestly elapsed between the forma- 

 tion of CEningen and that of Utznach ; so that we need not be 

 surprised to meet with a totally different flora in the Quaternary 

 period. It would be very interesting to learn what was the cha- 

 racter of the intervening period, and how the transition was 

 brought about ; and on this subject we may obtain some infor- 

 mation from the fossil plants of Italy. The Upper Miocene 

 flora of Northern and Central Italy, as exhibited in the gypsum- 

 quarries of Stradella and Guarene in Piedmont, in the burnt 

 and blue clays of the upper valley of the Arno in Tuscany, and 

 near Senegaglia, presents the same characters as those of the 

 Swiss Upper Miocene. There are found in the Italian Upper 

 Miocene flora the same species of liquidambars, evergreen 

 oaks, camphor-trees and laurels, Taxodia, Glyptostrobi, Planera, 

 planes, hornbeams, Sapindi, and walnut-trees as in the Swiss 

 flora. 



Above the Upper Miocene formation in the valley of the 

 Arno, in Tuscany, a yellowish-brown ferruginous sand occurs, 



