FOSSIL INFUSORIA. 37 



the shells of these creatures are thus found 

 coming into use, after the inhabitant has been 

 dead thousands of years. Dr. Mantell remarks, 

 in his ' Thoughts on a Pebble/- -" Investigation 

 has shown that a great proportion of the mass 

 of the (flinty) pebble, is actually composed of the 

 aggregated fossil skeletons of animalcules, so mi- 

 nute as to elude our unassisted vision, but which 

 the magic power of the microscope reveals to us, 

 preserved, like flies in amber, in all their original 

 sharpness of outline and delicacy of structure." 

 An extract from another author will prove that 

 chalk abounds also in remains of Infusoria.- 

 " Throughout the chalk beds there are layers of 

 flint, that is, masses of silex, or flint, of various 

 sizes, from a pea to a man's head, each lying 



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