66 GEOLOGY OF THE ISLE OF WIGHT. 



and river beds, and converted them into dry land. 

 The nature of those changes we now proceed to 

 consider. 



London eocene formation. — The London 

 Tertiary or Eocene deposits form the area on which 

 the metropolis is situated, as well as the sur- 

 rounding country to a distance varying from 

 ten to twenty or thirty miles. Around these 

 strata the Chalk presents a distinct boundary of 

 hills on the south, west, and north ; but on the 

 east the range is broken, and through this chasm 

 the Thames winds its way to the sea. 



From this geological character of the metropo- 

 litan district it results, that all the lines of rail- 

 way that proceed from London, traverse for the 

 first ten or twenty miles beds of clay, loam, and 

 loosely aggregated sand and gravel ; hence the 

 numerous slips that have taken place in the 

 embankments at New Cross, Wandsworth, Han- 

 well, &c. ; and in all these lines it is obvious 

 from the nature of the soil and the steepness of the 

 cuttings, that similar subsidences will again occur. 



Chalk formation. — The next geological 

 feature observable along the London railways, is 

 the. Chalk, which is invariably traversed by steep 

 cuttings and tunnels; as for example in the South- 

 eastern line, from Croydon to Merstham; and in 



