403 



EXPLANATION OF PLATES I. & II. 



No. 1. 



Plates I. and II. represent impressions of fossil leaves 

 found in a bed of potter's clay, belonging to a tertiary 

 lignite deposit near the mouth of Bear Lake River, de- 

 scribed in vol. i. p. 190. of the narrative. The leaves 

 must have been very numerous, and were evidently depo- 

 sited quietly from water turbid with fine potter's clay, 

 which forms the matrix. By the spontaneous burning of 

 the adjacent seams of lignite, the fossiliferous layer has 

 been subjected to heat of varying intensity, so that some 

 portions are semi-vitrified and rendered hard enough to 

 resist a file, while the greater part is in the condition of 

 moderately baked porcelain biscuit, and in some few 

 specimens the clay is but slightly altered. 



The impressions only, and none of the substance of the 

 leaves remain ; and owing to fusion of the leaves at their 

 margins from pressure, and the cracking of the clay matrix 

 from heat, none of the impressions of the larger leaves are 

 perfect in their outlines, though portions of the surface 

 are very delicately rendered so that the minute nervation 

 is distinctly shewn, and the existence of pubescence may 

 be made out. 



Table 1. fig. 2. is a representation of the impression of a 

 twig which has the character of Taxites acicularis, (Brong- 

 niart Prodr. 108, and "Descript. Geol. des Environs de 

 Paris, p. 362., t. ii. f. 13." Taxites foliis subdistichis, 

 linearibus obtusis). The leaf is scarcely half the length 

 of that of Taxus baccata, and is decidedly smaller than 



n d 2 



