196 FireLp CoLuMBIAN MusgEuM—GEoLoGy, VOL. I. 
In polarized light the yellow outer ring of the spherules remains 
dark during a revolution, indicating it to beopal. The interior portion 
assumes an appearance like that of granularquartz. This is similar to 
that described by Hovey as characterizing the interior of some of the 
spherules of the Pennsylvania oolite. The spherulitic interference 
cross is, however, clearly to be seen, and the optical character is nega- 
tive. Hence the method of formation can not be regarded as similar 
to that proposed by Hovey for the siliceous oolite, but is probably a 
simple spherulitic structure, in accordance with which any foreign 
matter, such as the opal, was arranged. The main portion of the 
chalcedony shows a typical radially fibrous structure. 

[DRAWN WITH CAMERA LUCIDA. | 
Fic. 1. Section from ‘* yolk” in ordinary Fic. 2. Same in polarized light. The 
light. Dark portion opal; light portion, in- opal becomes black; the chalcedony shows a 
cluding spherules, chalcedony. fibrous structure and the spherules interfer- 
ence crosses. 
X22. X22, 
A section of chalcedony from the veins of the region, studied for 
comparison, showed a similar strongly marked fibrous character and 
tendency to radial arrangement. 
The specific gravity of the specimen as a whole was found to be 
2.594, Or about that of chalcedony. io aa 
It is of course desirable, if possible, to obtain an explanation of 
the way in which so unique a case of petrifaction could occur, if 
petrifaction it be. 1 have been unable to find any account of a simi- 
lar occurrence as having been noted before. The fossil Chelonian 
eggs of Tertiary age from Auvergne, France, are simply shells filled 
with hardened mud. .The fossil eggs of the New Zealand birds are 
