8 GEOLOGICAL MEMOIRS. 



Italy, and the phsenomena which must have taken place when the 

 period of the tertiary formations succeeded to that of the secondary, 

 I think we may find the means of explaining, in a plausible manner, 

 whatever appears inconsistent out of Tuscany, with the beddings of 

 the macigno and of the alberese ; and also that we may understand 

 how formations containing secondary fossils, and others with tertiary 

 fossils were deposited during the same period. As it results from 

 many data, known to geologists, and as I shall more fully show here- 

 after, that the sea, by which the N.W. of Europe was covered during 

 the cretaceous period, did not communicate directly with that which 

 at the same period covered Italy and the Alps, these two seas may, 

 I think, have existed under such different circumstances as to 

 have felt, in a different manner, the effect of that catastrophe, or of 

 those changes of circumstances by which the animals and plants of 

 the tertiary period succeeded those of the secondary ; in conse- 

 quence of which the animals and the plants of the former period 

 survived in the one sea for a longer period than in the other, and, 

 at the same time, that state of things continued longer in operation 

 which caused those marine deposits peculiar to the earlier period. 

 In this manner we can understand the existence of contempora- 

 neous formations with secondary and tertiary fossils, and we may 

 also judge in what relation the mixed deposits may stand with re- 

 ference to the old and new series of causes. 



" It also appears to me, that under this supposition the newest 

 secondary formations, formed contemporaneously with the oldest 

 tertiary, cannot be considered otherwise than as cretaceous, being 

 merely the result of the local continuation of the physical con- 

 ditions of the existence of organic beings peculiar to the cretaceous 

 period. If this had really been the course of events, it must have 

 happened that where, as suggested, the conditions of the cretaceous 

 period were prolonged, and those of the tertiary epoch had not yet 

 commenced, the deposits peculiar to the latter epoch, and con- 

 temporaneously forming in other places, viz. the oldest tertiaries, 

 or the eocene, must be wanting ; and that is precisely what 

 occurs in our country, where, whilst those problematical upper se- 

 condary beds of which we are speaking are so fully developed, the 

 eocene, identical with those of the N.W. of Europe, are most rare, 

 or perhaps are altogether absent." 



The author then observes (p. 62) that further observations are 

 absolutely necessary before this question can be satisfactorily deter- 

 mined respecting the position of the macigno and the nummulitic 

 and hippurite limestones ; there is still reason to doubt the exact 

 correspondence as asserted of the nummulitic hippurite formation 

 of Italy with all the chalk of the north ; we have still to learn 

 whether all the Nummulites above the macigno are different from 

 those peculiar to the nummulitic limestone which underlies it, and 

 we must ascertain whether the supracretaceous Nummulites of the 

 Pyrenees belong to the same species as those which underlie the 

 macigno in countries nearest to Italy, or whether the former resemble 

 or differ from those in the upper part of the macigno. For the 



