LOWER TERTIARY. 1 63 



-tern part of North America. There is a simi- 

 lar geographical relation of the fossil shells in 

 the lower Tertiary rocks. They arc at first es- 

 sentially the shells oi the south coast oi Asia, 

 but afterwards include many forms which can 

 only be paralleled at the present day at our Antip- 

 odes, 50 that the life which is now found in many 

 distant regions, passed 1.1 SU< ages over 



the same area of the earth, and furnished fossils 

 to the r<>ck> which were laid down upon succes- 

 portions Of the sea-bed as it slowly moved 

 onward. 



The oldest tertiary strata in Europe are those 

 of Moils in Belgium, where the chalk is bent down 



into a trough, which received the w; shal- 



low iod than the chalk of 



at Britain, so that it carries an older deposit of 



tertiary age. In like manner thee and 



was riod than the coun- 



try in the meridian of Reading, SO that the beds 



in the eastern , the Thames basin are the 



Oldest in the British tertiary - The Mon- 



tiai. m include many w hich 



are common to tin- the lower tertiary 



period. 



Thantt Sands. 

 The Thanet Sands are the oldest tertiary bed 



in Great Britain. They are a w< iped de- 



posit of sand which occurs in the east of the 

 trough known as the London basin. It is 90 feet 

 thick at Canterbury and Heme Bay, and thins 

 westward, being absent to the west of a line from 

 Leatherhead to Hertford. It is a marine de- 

 posit, abounding in shells, most of which live on 

 into the London clay. There is a Pholadomya, a 



