MODE III. LIMESTONE, 453 



pious memorials of the miracles of saints. If they 

 at all exist at present, they are said to be found 

 microscopic in the Adriatic sea; but a contorted 

 species of nautilus has often been confounded 

 with Cornu Ammonis. The petrified are styled 

 Ammonites, the Greek termination in this and 

 the other shells marking their stony nature. Am- 

 monites occur of all sizes, from half an inch in 

 diameter, as those which form the singular Dor- 

 chester marble, to six feet, or the size of a coach- 

 wheel, as some have been found immersed and 

 converted into chalk at Margate. 



The nummulites, or porpites, occur in the lime- 

 stone of Egypt and of France, being thin shells, 

 or rather movable opercules or covers to protect 

 some shell-fish. Belemnites*, another embarrass- 

 ing form, are generally found detached. Entro- 

 chites, or joints of the sea-star, are very common. 

 The encrinites, other joints, resemble lilies. 



To proceed to the UNIVALVE shells : nautilites 

 abound in many limestones and marbles; and 

 sometimes retaining their original lustre, impart 



* Perhaps these may be spines of a large pelasgian sea-urchin. 

 The porpite has at last been observed alive in the South Sea. See 

 the curious plates to the voyage of Peron, Paris 1808, 4 to. ; where 

 the rich and interesting delineations of the zoophytes and mollusks 

 are very new and striking. 



