Ch. XVIL] PISOLITIC LIMESTONE OF FEAjSTCE. 235 



between the Eocene and recent periods, to the history of which the last 

 seven chapters have been devoted. Several fragmentary deposits have 

 been met with here and there, in the course of the last half century, of an 

 age intermediate between the white chalk and the plastic clays and sands, 

 of the Paris and London districts, monuments which have the same kind 

 of interest to a geologist, which certain mediaeval records excite when we 

 study the histoiy of nations. For both of them throw light on ages of 

 darkness, preceded and followed by others of which the annals are com- 

 paratively well known to us. But these newly discovered records do not 

 fill up the wide gap, some of them being closely allied to the Eocene, and 

 others to the cretaceous type, while none appear as yet to possess so dis- 

 tinct and characteristic a fauna, as may entitle them to hold an indepen- 

 dent place in the great chronological series. 



Among the formations alluded to, the Thanet Sands of Prestwich have 

 been sufficiently described in the last chapter, and classed as Lower Eo- 

 cene. To the same tertiary series belong the Belgian formations, called 

 by Professor Dumont, Landenian and Heersian, although these are prob- 

 ably of higher antiquity than the Thanet Sands. On the other hand, the 

 Maestricht and Faxoe limestones are very closely connected with the 

 chalk, to which also the Pisolitic limestone of France has been recently 

 referred by high authorities. 



The Lower Landenian beds of Belgium consist of marls and sands, often 

 ■containing much green earth, called glauconite. They may be seen at 

 Tournay, and at Angres, near Mons, and at Orp-le-Grand, Lincent, and 

 Landen in the ancient province of Hesbaye, in Belgium, where they 

 supply a durable building-stone, yet one so light as to be easily trans- 

 ported. Some few shells of the genus Pholodamya, Scalaria, and others, 

 agree specifically with fossils of the Thanet Sands ; but most of them, 

 such as Astarte incequilatera, Nyst, are peculiar. In the building-stone 

 of Orp-le-Grand, I found a Cardiaster, a genus which, according to 

 Professor E. Forbes, was previously unknown in rocks newer than the 

 cretaceous. 



Still older than the Lower Landenian is the marl, or calcareous glau- 

 conite of the village of Heers, near Waremme, in Belgium ; also seen at 

 Marlinne in the same district, where I have examined it. It has been 

 sometimes classed with the cretaceous series, although as yet it has 

 yielded no forms of a decidedly cretaceous aspect, such as Ammonite, 

 Baculite, Belemnite, Hippurite, &c. The species of shells are for the 

 most part new ; but it contains, according to M. Hebert, Pholodamya 

 cuneata, an Eocene fossil, and he assigns it with confidence to the tertiary 

 series. 



Pisolitic limestone of Prance. — Geologists have been still more at 

 variance respecting the chronological relations of this rock, which is 

 met with in the neighborhood of Paris, and at places north, south, 

 east, and west of that metropolis, as between Vertus and Laversines, 

 Meudon and Montereau. It is usually in the form of a coarse yellow- 

 ish or whitish limestone, and the total thickness of the series of beds, 



