Ch. XVII.] PISOLITIC LIMESTONE OF FRANCE. 313 



throw light on ages of darkness, preceded and followed by others of 

 which the annals are comparatively 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 distinct and characteristic a 

 fauna as may entitle them to hold an independent 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 Eocene. To the same tertiary series belong the Belgian for- 

 mations, called by Professor Dumont, Landenian and Heersian, 

 although the latter may be 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 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 transported. Some few shells of the genus Pholadomya, Sca- 

 laria, 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 

 glauconite, 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, Pholadomya cuneata, an Eocene fossil, and he assigns it with 

 confidence to the tertiary series. 



Pisolitic . limestone of France. — 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 yel- 

 lowish or whitish limestone, and the total thickness of the series of 

 beds already known is about 100 feet. Its geographical range, ac- 

 cording to M. Hebert, is not less than 45 leagues from east to west, 

 and 35 from north to south. Within these limits it occurs in small 

 patches only, resting unconformably on the white chalk. It was 

 originally regarded as cretaceous by M. E. de Beaumont, on the 

 ground of its having undergone, like the white chalk, extensive denu- 



