346 EOCENE, MIOCENE, AND 



lizcd spicula, sometimes of a calcareous,, at others of a 

 siliceous, nature." Thus, a frame of siliceous matter 

 being formed by the living animal, a deposition of the 

 same substance is continued after death. 



Sea-urchins and star-fish, and numerous fossil shells, 

 are found in these beds, which, however, differ materially 

 from the remains of the same animals found in the 

 earlier formations. A vast number of new species and 

 genera of fish are also discovered in the chalk. 



Nearly all the animals and plants which existed up to 

 this period are now extinct, although they have some 

 imperfect representatives at the present day. 



The uppermost group, which has been called the 

 supercretaceous or tertiary formation, appears in our 

 island to have been formed during four great eras, as 

 we find fresh-water deposits alternating with marine 1 

 ones. The term eocene, which is the first or oldest 

 deposit ; miocenc, which is the second ; pliocene, which 

 is the third ; and the newer pliocene, which is the fourth 

 and last, have been applied to these formations, the 

 names referring to the respective proportions of existing 

 species found among their fossil shells.* 



All these formations show distinct evidence of their 

 having been deposited from still or slowly-flowing deep 

 waters. Thus the eocene appears in the Paris basin, 

 formed clearly at an estuary, in which are mingled some 

 interesting fresh-water deposits; in the lacustrine 

 formations in Auvergne ; also at Aix ; and in the north 

 of Italy. It appears probable that, in the formations 

 generally termed eocene, both fresh-water and marine 

 deposits have been confounded, and several formations 

 of widely-different eras regarded as the result of one. 

 We have not yet been furnished with any distinct and 

 clear evidence to show that the deposits of the Paris 



* Geology, Introductory. Descriptive, and Practical: by Prof 

 Ansted. vol. ii. p. :l:l. 



