Apr. 1899. A Fossit Ecc rrom SoutH DAkoTA—FArRRINGTON. 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matter of the egg, which has not -as~yet been replaced by siliceous 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—yjoin, 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 
Oolite of Pennsylvania, which has been described by Barbour and 
Torrey* and E. O. Hovey.t: 
* Am. Jour. Sci., 3d Ser., Vol. XL, p, 246. 
+ Bull. Geol. Soc. of America, Vol. V, p. 627. 
