APPENDIX. 103 



ness. The towns of Richmond and Petersburgh, in 

 Virginia, are built upon this infusorial sandstone. 



All the species of animalcules found in the Richmond 

 earth are marine ; and many of them belong to genera, 

 (if not to species), that inhabit the present seas, al- 

 though the position of these American strata proves 

 that they are referable to a very remote geological 

 epoch. Some of the prevalent Richmond forms, (the 

 Coscinodisci, or sieve-like disks), live in the British 

 Channel ; and my son, (Mr. REGINALD MANTELL), de- 

 tected in the mud of the quicksands along the shore at 

 Brighton, the shields of numerous recent Coscinodisci, 

 associated with fossil Infusoria washed out of the neigh- 

 bouring chalk-cliffs. 



Another interesting discovery in connexion with this 

 subject may here be noticed. The common scallops, as 

 well as other mollusks, feed on Infusoria, and their 

 stomachs often contain thousands of shells, which, 

 being siliceous, have resisted the process of digestion. 

 A glass slide mounted with a few particles of the undi- 

 gested contents of the stomach of a scallop, presents an 

 assemblage of infusorial shells, apparently identical with 

 those forming the Richmond earth*. So close, indeed, is 

 the analogy, not only of the individual shields, but even 



* Mr. HAMLIN LEE first noticed this interesting fact. 



