356 THE WONDERS OF GEOLOGY. Lect. IV. 



delineated in the drawing, Lign. 77, can be removed, so as 

 to expose the bones of the plastron, or sternal plates, be- 

 neath. This fossil is six inches in length, and three and a 

 half in breadth. 



40. Summary. — The characters of the Cretaceous For- 

 mation, as shown by these investigations, are those of a 

 vast oceanic basin, filled up with organic and inorganic 

 debris, and innumerable remains of the successive genera- 

 tions of marine animals which lived and died in its waters, 

 through periods of incalculable duration. 



The fossil fuci indicate that the chalk ocean possessed the 

 usual marine flora ; while the drifted masses of wood bored 

 by teredines, and the fir-cones, stems of cycadeous plants, 

 leaves of ferns, and bones of terrestrial reptiles, prove that 

 its shores were bounded by dry land, which was clothed 

 with forests, and inhabited by colossal oviparous quadru- 

 peds. Of the higher orders of animals no unquestionable 

 relics have yet been discovered. 



a tabular arrangement of the fossil fishes of the chalk of the 

 South-East of England, in the Mantellian Museum at Brighton.* 



{From " Recherches sur les Poissons Fossiles," by M. Agassiz.) 



" Tout le monde sait que le Musee de M. le Dr. Mantell a Brighton est une collection classique 

 pour lacraie, et la formation Veldienne. Les soins minutieux que M. Mantell a donnas depuis 

 bien des amines a ces fossiles, les ont rendus plus parfaits que tous ceux des autres musses : car 

 souvent il est parvenu a les detacher entierement de la rochedans laquelle ils se trouvaient ; ou du 

 moins a les produire en relief, en dStachant toutes les matures solides qui recouvraient les parties 

 les mi^ux conserves de Tanimal." 



Order I. — The Placoidians, (from 7rAa|, a broad plate.) The skin, 

 covered irregularly with enamelled plates, sometimes of a large size, 

 but frequently in the form of small points, as in the shagreen on the 

 skin of sharks, and the tubercles on the integuments of rays. 



* Now in the British Museum. 



