1848.] MURCHISON ON THE STRUCTURE OF THE ALPS. 2/7 



one region to another, and above all the accompanying phaenomenon 

 of an almost entire disappearance of organic remains, have neces- 

 sarily involved them in much obscurity in Liguria, Modena and 

 Tuscany. As a whole, there is indeed a strong lithological re- 

 semblance, as before said, between the rocks called macigno by the 

 Italians, and the flysch and Wiener sandstein of the Swiss and Au- 

 strian geologists. In the Apennines, as in the Alps (I have already 

 alluded to it in the Apuan ridge), there is a fine-grained small mica- 

 ceous sandstone which much resembles the ordinary macigno, whose 

 exact age. whether cretaceous or eocene, may be doubtful ; but I now 

 simply treat of that macigno which, wherever there have been no in- 

 versions, is either intercalated with, or superposed en masse to, the 

 nummulitic rocks. If we appeal to the environs of Florence, we see 

 that, however wanting in a clear cretaceous base-line in the vicinity 

 of that city, the whole of the Tuscan series of alberese and macigno 

 sandstones repose upon secondary limestone (chiefly Jurassic) in the 

 Pisan hills on the west, at Monte Cetona and Campiglia on the 

 south, and in the central Apennines of Monte Verame and Citta di 

 Castello on the east. In defining the relations of the component 

 parts of this group, I have already expressed my belief, that in parts 

 of Tuscany the lower portion is probably the non-fossiliferous repre- 

 sentative of the upper portion of the cretaceous system. In fact, the 

 term "alberese" is so loosely applied to every light-coloured lime- 

 stone, pure or impure, which dips under or alternates with macigno, 

 and which may happen to contain fucoids, that it would be very 

 hazardous, in tracts so void of organic remains, to define the neat 

 limits between secondary and tertiary. We have not here, as in 

 the Alps, either a neocomian limestone with its fossils to represent 

 the lower greensand of the English, nor anything like the Alpine 

 equivalents of upper greensand and chalk. But, if so obscure in the 

 descending order (and he who crosses the chain from Bologna to Flo- 

 rence will admit this to be the case), these tracts have, however, one 

 strong point of comparison with the Alps in the lithological resem- 

 blance of their upper macigno to the flysch of the Swiss. They 

 farther resemble certain Alpine tracts in having no rigid boundary or 

 break between the lowest strata in which nummulites occur, and the 

 beds above and below them. The best proof of this is, that Pro- 

 fessor Pilla described as one natural physical group, which he termed 

 " Etrurian," that which, on further inquiry, he conceived to be com- 

 posed in its lower part of strata referable to the chalk, and in its 

 higher part of a peculiar intermediary formation. As this Etrurian 

 system {so named from the country in all Europe most deprived of 

 organic remains) is thus composed of both secondary and tertiary 

 strata, it is manifest that the term is geologically inadmissible. 



Whilst then the lowest alberese, and some macigno, may remain as 

 very ill-characterized cretaceous rocks, the upper Etrurian of Pilla is 

 in fact nothing more than the eocene group of the Alps, hke which 

 it contains, in some localities, zones of nummulitic limestone, and is 

 further surmounted by vast accumulations of macigno sandstone. 



The nummulitic limestone of Mosciano, near Florence, having been 



