408 Mr. Murchison on the Tertiary and Secondary Rocks 



in different parts of the north of Italy. Brocchi having de- 

 scribed the whole of these deposits under the head of Sub- 

 apennine* ; and thus formations of the age of our London clay 

 being confounded with those blue marls containing a variety 

 of recent shells, it now becomes quite essential to state that the 

 inferior members are essentially different from the superior in 

 zoological contents ; it being in the upper beds only that we find 

 a large proportion of shells of the present sea. To this lat- 

 ter epoch belong the conglomerate sands and marls of Asolo 

 and Bassano ; and the strata which succeed, offer (amidst the 

 ie\f specimens which my hurried examination permitted me 

 to collect), some species resembling those of the Bourdeaux 

 basin ; whilst by far the greater number of the shells enumerated 

 in the oldest members of marl and limestone, near Possagno 

 and on the Brenta, are identical in species with those of the 

 Calcaire grossier of Paris, and the London clay. The lowest 

 beds of this formation both in the north of Europe and in Italy 

 are very similar in containing not only many of the same spe- 

 cies of mollusca, but also identical species of nummulites, ca- 

 ryophyllia, &c. Nor can it be urged that the multilocular fos- 

 sils of these inferior strata are also found in the higher tertiary 

 deposits of Italy, for the microscopic shells of Sienna figured 

 by Soldani differ entirely from those of the Calcaire grossier 

 both in family and species. 



Now although we may compare the nummulite rock of Bas- 

 sano with the Calcaire grossier of the London and Paris basins, 

 we cannot extend the comparison to the subjacent strata : for 

 unlike certain parts of the Paris basin, where a formation distin- 

 guished by its freshwater and terrestrial remains is interposed 

 between the Calcaire grossier and the chalk, the plastic clay is 

 entirely wanting near Bassano, and there also the representative 

 of the Calcaire grossier is in conformable apposition to the 

 scaglia or rock containing ammonites f: so that in this por- 

 tion of the earth's crilst we have no trace of any interval of 

 repose between the secondary and tertiary epochs when, as 

 some geologists have imagined, the ocean subsided, and the 

 land was left dry for terrestrial and fresh- water productions 



* Conchiologia Subapennina, vol. i. p. 97. 



•f It may be remarkeil, that the [ilastic clay is not only absent in the 

 north of Italy but also in most parts of England, and in some situations 

 in France, provided that formation is to be defined as one o{ fresh-water 

 origin. In the Isle of Wight, and at Reading, it is well known that the 

 lowest tertiary beds are exclusively charged with marine exuvias. If zoo- 

 logical evidence therefore, be considered decisive, the plastic clay cannot 

 be viewed as a distinct and extensive formation resulting from any general 

 cause, but rather as an accidental aestuary deposit, produced by local cir- 

 cumstances. 



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