Apr. 1899. A Fossil Egg from South Dakota — Farrington. 195 



white opalescent substance quite homogeneous except for occasional 

 darker spherules, which show a concentric structure similar to those 

 of the other portion. The opalescent substance appears both in its 

 chemical and optical characters to be true opal. It is considerably 

 cracked. It is infusible B. B., but has a hardness less than 7. On 

 heating in the closed tube it gives off 'a little water, turns black in 

 spots and emits a distinct odor of burning nitrogeneous matter. 

 This I conjecture to come from some of the original organic 

 matter of the egg, which has not as yet been replaced by siliceous 

 matter. As such an occurrence had not come within my observation 

 before, I thought it well to test some other petrified substance to learn 

 if it contained any organic residue. Accordingly, fragments of the 

 well-known petrified wood from Sonoma County, California, were put 

 to a similar test, and somewhat to my surprise an odor of smoking 

 wood was distinctly given off. It therefore seems probable that in 

 many petrified substances some of the original organic matter may 

 remain imprisoned. 



In order to determine whether any remains of cell structure were 

 to be observed, a fragment from the portion where the " white" and 

 "yolk " — in other words, the chalcedony and opal — join, and which 

 showed as well a spherule of chalcedony, was ground thin for micro- 

 scopic examination. As shown by the drawings, Figs. 1 and 2, noth- 

 ing like cell structure is to be seen in the section. The chalcedonic 

 portion shows several spherules, but these do not differ in character 

 from those usual to chalcedony. In the portion made up of opal an 

 elongated cavity is to be seen which suggests in form a compressed 

 air bubble. This is lined with two successive layers which may fol- 

 low some membranous structure, but of this there is no certainty. 

 The portion of the section made up of opal, when viewed in ordinary 

 light, is of a yellowish-brown color, and shows no other structure 

 than that mentioned. In polarized light it becomes wholly dark, 

 showing its amorphous and singly refracting character. The portion 

 made up of chalcedony is colorless in ordinary light except for the 

 spherules previously mentioned. These are bounded by a thin, yel- 

 low ring, within which is a transparent area, and within this, making 

 up the central portion, is another yellow mass, having a distinctly 

 radiated fibrous structure. The general appearance of the spherules 

 in ordinary light is thus very much like that of those of the siliceous 

 oblite of Pennsylvania, which has been described by Barbour and 

 Torrey* and E. O. Hovey.f 



• Am. Jour. Sci.. 3d Ser., Vol. XL, p, 246. 

 t Bull. Geol. Soc. of America. Vol. V, p 627. 



