I..] 



SPRINGS. 



23 



the rocks in question have been cut through so as to expose 

 clean-cut surfaces, and hence such diagrams, which are 

 constantly used in writings on the structure of the earth, 

 are termed sections. Natural sections are frequently exposed 

 ia river-beds, sea-cliffs and inland valleys ; whilst artificial 

 sections are seen in wells and shafts, in mines and quarries, 

 and especially in railway-cuttings. A good general notion 

 of the character of the rocks forming a given country may 



' ::^^^?^>.-:s^^^^'^^-^^ -''%<^^-';C^'^^-' 



Fig. 6. — Formation of a spring. 



often be gained, during a railway journey, by observing the 



cuttings along the line.' 



1 Some good geological sections may be seen in railway cuttings in 

 tlie neighbourhood of London. Thus, in travelling by the North 

 Western Railway to Watford, the passenger may observe the London 

 clay ; and, further on, the Lower London Tertiaries overlying the 

 chalk. On the Great Western Railway, the route to Maidenhead passes 

 over the brick-earlh and gravel which overlie the London Clay, and, at 

 Windsor, the chalk is exposed, but not on the railway. To the south 

 of London, some good sections may be seen in the cuttings on the North 

 Kent Railway in the neighbourhood of Lewisham and Charlton, where 

 the sandy deposits, known as the Thanet Sands, are exposed. A 

 journey to Reigate, on the Brighton line, carries the passenger over the 

 London clay, the chalk, and the beds below the chalk known as 

 Greensand. For other sections see Whitaker's Guide to the Geology oj 

 London, • 



