BLUE CHALK MARL. 89 



The specimens delineated are from Kingmer. 



Ammonites. 



The ammonites of this deposit, are equal in elegance and beauty to 

 any hitherto known. When first collected, they retain in general a 

 considerable portion of the original shell, with its nacreous covering 

 heightened by the changes it has undergone in the mineral kingdom. 

 They are very iridescent, and in many instances derive a golden lustre 

 from an impregnation with sulphuret of iron, that renders their appearance 

 remarkably splendid *. Their cavities are filled with pyrites, indurated 

 marl, and argillaceous ironstone, and from the excellent state in which 

 the septa are preserved, their foliaceous structure is shown in numerous 

 examples. 



In the Dictmmaire d'Histoire Naturelle, mention is made of a bed of 

 clay, in the vicinity of Moscow, where ammonites occur under similar cir- 

 cumstances, and apparently in the same state of preservation -j-. 

 15. Ammonites splendeiis. Tab. xxi. figs. 13, 17. 



Involute, depressed, carene flat, with carinated margins ; volutions 

 three or four, deeply inserted, flat, transversely radiated ; radii depressed, 

 curved towards the aperture ; a row of distant elongated tubercles on the 

 inner margin ; aperture sagittate ; dissepiments fohaceous ; siphunculus 

 internal. 



The external volutions rapidly increase in breadth, the inner ones 

 being three-fourths concealed. Two or three radii arise from each tu- 



* The pyrites upon which the beauty of these fossils principally depends, undergoes de- 

 coniposition upon exposure to the air, even for a short period ; a circumstance that occasions 

 the destruction of nine-tenths of the specimens, after they have Iain in the cabinet of the col- 

 lector but a fevr weeks. I have employed various means for their preservation, but without 

 success ; varnishes, gum water, albumen, &c. destroy their lustre, and give them an impleasant 

 appearance. 



f " J'en ai vu d'immenses quantites des ammonites dans les couches d'argile qui forment le 

 I'ivage de la Moscoua, pres de Moscou, a cinq ou six pieds seulement au-dessous de la surface 

 du sol. Elles sont toutes d'une grandeur mediocre et n'excedent pas cinq a six pouces de 

 dianietre ; elles sont de Tespece qui est articulee et decoree d'arborisations. Rien n'est si beau 

 que ces cornes d'ammon dans I'instant ou on les retire de leur gite ; elles sont revetues d'une 

 couche pyriteuse couleur d'or et gorge de pigeon ; mais des qu'elles ont pris I'air, elles s'ef- 

 fleurissent et tombent en miettes. Elles sont melees des beaucoup de belemnites, qui sont 

 egalement d'une volume mediocre. Diet. d'Hist. Nat. p. 332. tome vi. 



