xin.] SLOW MOVEMENTS OF THE LAND. 213 



have been variations of level to a much greater extent, at 

 more remote periods, is abundantly testified by the strata in 

 almost any part of the country. London, for example, is 

 seated on clay, which, as already pointed out, must have been 

 deposited under water, in the state of mud. But as this 

 clay contains, in many parts, the remains of marine shell- 

 fish, such as the nautilus, there can be no doubt that the 

 mud in such places must have been originally thrown down 

 out at sea. The clays, sands, and other deposits below the 

 London clay, already referred to under the name of the Lower 

 London Tertiaries (p. 32), have been formed, some in salt and 

 others in brackish water, as is testified by the character of the 

 shells which they contain. As to the chalk, which lies in a 

 mass of vast thickness immediately beneath these deposits, 

 it will be shown, in a subsequent chapter, that it abounds 

 with the remains of creatures which once lived in the depths 

 of the sea. If, then, these rocks are, in great measure, 

 nothing but old sea-bottoms, it is clear that great upward 

 movement must have taken place to raise them into their 

 present situation. 



But this is not all. The rocks have not only been up- 

 lifted, but in many cases have been subjected to some dis- 

 turbing action by which they have been more or less contorted. 

 The section in Fig. 11, p. 31, shows that the strata beneath 

 London lie in a gentle hollow, purposely exaggerated in the 

 diagram, but still sufficiently marked in nature to suggest the 

 name of " London Basin." Supposing they had been ori- 

 ginally deposited in a depression of the sea-bottom, the 

 layers would have been thrown down almost horizontally, as 

 in Fig. 60 ; and not in curved layers of equal thickness as in 

 Fig. 61, such as are really found in nature. The present 

 position of these rocks is therefore explained by supposing 

 that the strata were originally horizontal and have been 



