THE EARTH. 4-1 



ed by M. Buffon, supposes them to have been de- 

 posited in the earth at the time of the Crusades, by 

 the pilgrims who then returned from Jerusalem ; 

 who, gathering them upon the sea-shore, in their 

 return, carried them to their different places of 

 habitation. But this conjecturer seems to have 

 but a very inadequate idea of their numbers. At 

 Touraine, in France, more than a hundred miles 

 from the sea, there is a plain of about nine leagues 

 long, and as many broad, from whence the pea- 

 sants of the country supply themselves with marl 

 for manuring their lands. They seldom dig 

 deeper than twenty feet, and the whole plain is 

 composed of the same materials, which are shells 

 of various kinds, without the smallest portion of 

 earth between them. Here then is a large space, 

 in which are deposited millions of tons of shells, 

 which pilgrims could not have collected, though 

 their whole employment had been nothing else. 

 England is furnished with its beds, which though 

 not quite so extensive, yet are equally wonderful. 

 " * Near Reading, in Berkshire, for many suc- 

 ceeding generations, a continued body of oyster- 

 shells has been found through the whole circum- 

 ference of five or six acres of ground. The foun- 

 dation of these shells is a hard rocky chalk ; and 

 above this chalk the oyster-shells lie in a bed of 

 green sand, upon a level, as nigh as can possibly 

 be judged, and about two feet thickness." These 

 shells are in their natural state, but they are 

 found also petrified, and almost in equal abun- 

 dance! in all the Alpine rocks, in the Pyrenees, 



- Phil. Trans. voLii. p. 427. f Buffon, voL i. p. 407. 



