

ANCIENT AND MODERN DEPOSITS. 91 



often thin and irregular sandstones and conglomerates of earlier ages ; 

 the finer clays which fill the broader and deeper hollows of our 

 seas, because such fine sediments are held long in suspension by 

 water, are quite similar in position to the older argillaceous de- 

 posits ; and our modern coral reefs and the shell beds which 

 accompany them, produced in clear pelagic waters, unmixed with 

 sediments from the land, are in many respects exactly the repre- 

 sentations of the old limestones of Wenlock, Bakewell, Calne, and 

 Orford. 



