70 THE WEALDEN DEPOSIT. 



7. This formation is composed of alternate layers of limestone 

 sand, more or less ferru'ginous, and clay, the deposits of which art 

 sometimes extremely thick. There are entire beds of limestone 

 composed of paludi'nse, constituting what is named Purbeck lime' 

 stone. The laminae of argilla'ceous matter are often covered by 

 cy'clades and anodo'ntx, and we find disseminated a great number 

 of small cypris. There are many species of fresh water fishes, 

 the remains of fluviatile tortoises, mingled with marine and terres- 

 trial saurians, among which is the monstrous i'guanodon, w r hich 

 must have been thirty feet in length, to judge from the size of its 



bones. In this formation are 

 found also, in the dirt of the Isle 

 of Portland, the sili'cified stems 

 of cyca'deas (Jig. 124), standing 

 erect in the midst of the earth, 

 of which the deposit consists ; 

 various species of con'ifers, equi- 

 sita'ceae, and ferns are also met. 

 The remains of birds of the order 

 Fig. 124. Mante'llia nidifo'rmis. of gra'Dese (waders)also exist, but 



no mammals, although we have seen them in the marls of the 



o'olite (jig* 81, 82). 



8. It is believed that the clays in the environs of Boulogne, 

 which seem to be continuous w r ith those of England on the south- 

 ern side of the Channel, may be referred to the wealden deposit, 

 as well as those of Forges and of Savigny in the country of Bray, 

 where paludine limestones like those of Purbeck have been found. 

 It is very certain, according to the observations of M. Leymerie, 

 these deposits are connected with those in the department of Aube, 

 and form part of the superior neocomian clays : if there are indi- 

 cations of fresh water deposits, they prove the connection between 

 the wealden formations and those of this epoch. 



9. According to English geologists, the wealden formation is 

 below the neocomian, and is, consequently, older and not precisely 

 contemporaneous with it. 



10. Above the neocomian and wealden formations there is a 

 group of deposits generally termed Green Sand, consisting of two 

 arena'ceous beds, with a parting of clay called gaitlt. The green 

 sand formation receives its name from the prevalence of smal 1 

 ^rreen particles of si'licate of iron distributed through the sand. It 

 is found in New Jersey. In England it is divided into lower green 

 &and, gault, and upper green sand. This group consists of white 



7. What is Purbeck limestone ? 



8. Whai is the extent of the Wealden formation ? 



9. Which deposit lies above, the Neocomian or Wealden ' 



10. What is found next above the Wealden and Neocomian ? From what 

 dues green sand obtain its name ? How is it divided? 



