127 



gratulating myself on having declined the arduous attempt, of adapt- 

 ing a nomenclature to the substances examined in this volume, or of 

 disposing them in a systematic arrangement. Even to one who possessed 

 all the necessary qualifications, success, in the present state of our 

 knowledge, could not be assured. For such is the variety of form and 

 of organization discoverable in these substances, as to mock all en- 

 deavours at arranging them, or even comparing them with any known 

 recent substance. 



Analogy, indeed, proves their existence to have depended on the 

 powers of animal life, but it seldom helps us any farther; since, with 

 respect to many of them, we can find no corresponding species nor 

 genus, under which, known existing beings are disposed, which will 

 also allow of their admission. New terms must therefore be also re- 

 quired to designate these hitherto unknown substances; but these can 

 neither be formed nor applied, until illustrative specimens, and farther 

 observations, have supplied a more correct knowledge of these sub- 

 stances, and of the circumstances by which their 'relationship with 

 each other should be determined. 



Tiiese observations particularly apply to the fossils which have been 

 treated of in this letter; since considerable difficulty must occur in 

 the endeavour to arrange them, either according to their figure or their 

 external structure. If the fungiform or cup-like figure were to be takea 

 as the distinguishing character, we should then find, that under this 

 form would be classed substances, differing very materially in their struc- 

 ture. The fungiform fossil, Plate VIII. Fig. 5, is formed of lamellae 

 connected with each other by inosculation. The one, Plate XI. Fig. 

 7. is composed of lamellae perpendicularly disposed, and so con- 

 nected by small transverse septa or processes, as to produce po- 

 lygonal terstices. The specimen, Plate XI. Fig. 5, from France, 

 is formed of innumerable tubuli, extending horizontally from the 

 inner to the outer suface ; their bases being on the outer, and their 

 other, the open terminations, being on the inner surface. Lastly, the 



