276 Prof. L. Pilla on the Etrurian Si/stem, 



1st. That the northern chalk is connected with the nummii- 

 litico-hippuritic limestone of the south of Europe, but never 

 with the macigno, which is above this. 



2nd. That the nummulitico-hippuritic limestone of Italy re- 

 presents all tiie northern cretaceous limestone; in the greatest 

 part the upper and lower greensand, and only in certain lo- 

 calities the white chalk. 



3. Independence of the Macigno Formation. 



If we admit that the nummulitico-hippuritic limestone of 

 the Mediterranean is the representative of the whole of the 

 chalk of the north of Europe, and that the macigno is super- 

 posed on this limestone, we must admit also that this forma- 

 tion constitutes a peculiar de})osit and one wholly distinct from 

 the chalk. This distinction is based on all the characters which 

 establish the independence of a formation, — on the mineralo- 

 gical characters, on the superposition, and on the fossils, as 

 we shall presently remark. 



The macigno of Tuscany and of Liguria, which is the most 

 classic, has no mineralogical analogy with the chalk of the 

 north-west of Europe ; the rocks which compose it have quite 

 peculiar characters. To this difference we must add another 

 very remarkable circumstance ; the flint, which appears to be 

 a substance almost inseparable from the upper northern chalk, 

 is entirely wanting in the Italian macigno ; and, although this 

 circumstance may be considered in general as of little value, it 

 is of great weight in this special case. There have likewise not 

 been found any of those green particles which are frequently 

 met with in the cretaceous greensand of the north, whence it 

 takes its name. 



With regard to the superposition, we have seen, first, that 

 the macigno must be considered as above the white chalk. 

 In the second place, we have observed that the different beds 

 of the nummulitico-hippuritic limestone, which are parallel to 

 the beds of the northern chalk, are connected together by in- 

 sensible gradations, which proves that they have been deposited 

 in the same sea, and under the same circumstances; whilst 

 the macigno is always separated from these deposits by a well- 

 marked line and by different topographical circumstances, and 

 never mixes with them, which is an evident sign that it has been 

 deposited in a different sea, and under different circumstances. 

 Lastly, if one of the principal characters of the independence 

 of a formation is its superposition on rocks of various ages, 

 this is verified in the macigno more than in any other forma- 

 tion, because it is seen superposed at one time on the nummu- 

 litico-hippuritic limestone (Liguria), at another on the Jura 



