GEOLOGY. 93 



This series exhibits the remains of animal and vege- 

 table life approaching progressively to those of the 

 present day. It would seem, from the alternate depo- 

 sition of marine and freshwater strata in the Secondary 

 Series, that the earth was then, at least in various places, 

 alternately covered by the sea and by freshwater. But 

 this is particularly evident in those immense basins of 

 rocks discovered by later geologists, the principal of 

 which are the Paris basin, the London basin, and the Isle 

 of Wight basin. First there is a marine deposit, then 

 there is a freshwater stratum ; again there is another 

 marine deposit, and fourthly, another freshwater stra- 

 tum : and over these an alluvial soiL 



The EOCENE* FORMATION is so called from its ap- 

 pearing to be the commencement of a new order of 

 things. Fossils of testacea, which were then called into 

 existence, have continued to inhabit the ocean until the 

 present time. It is supposed that great alteration must 

 have taken place in the temperature of the earth's sur- 

 face since that period and the present time, as many of 

 the testacea which were then found on the British 

 shores, are now only found within the Tropics. 



The Plastic Clay and London Clay are marine forma- 

 tions. The London Clay is so called because London 

 stands as it were upon it. These clays pass into marl, 

 and are covered with gravel, and are 50O or 600 feet or 

 more in thickness. The Hampshire freshwater formation, 

 consists chiefly of marls. The Bagshot Sands are a 

 marine deposit. 



The MEIOCENE FORMATION! does not exist in Eng- 

 land, unless the English Crag is referred to it. Lignite, J 

 a kind of imperfect coal, is found, in Germany in this 

 formation. 



* Eocene, from sw;, the break of day, and XXM; new. 



f Meiocene, from pen* less, and xao:,- new ; in opposition to the 

 ext formation. 



f Wood has been found in Languedoc partly converted to jet. 

 Trees have also been found converted to jet, and so entire as to mark 

 their species. A petrified forest has been discovered under the banks 

 of the Tiber. Forests of standing trees have been found in Yorkshire 

 and in Ireland imbedded in stone. Trees have been found in Lapland 

 and Siberia, converted into iron ore and carbonate of copper. 



