194 Field Columbian Museum — Geology, Vol. i. 



detail. The portion which may sufficiently be designated as the shell, 

 was found to be translucent chalcedony similar to that of the main 

 mass, or what may be called the white, and for the most part con- 

 fluent with it. It is, however, dark brown to black in color. On 

 heating to redness this color disappeared, indicating organic matter 

 to be the coloring ingredient. In one or two spots the shell was not 

 homogeneous throughout, a thin white layer separating it from the 

 main portion. This, on testing, proved to be carbonate of lime, indi- 

 cating that here some of the original shell had not been replaced by the 

 petrifying siliceous solutions. No definite structure or markings could 

 be distinguished on the shell. While generally smooth in outline, under 

 a lens it is seen to be rough and porous, owing doubtless to the action 

 of the infiltrating waters. The original markings, if any, must have 

 been destroyed by such an action. 



The portion designated as representing the white of the egg is, 

 as has been said, made up of pale gray translucent chalcedony. It is 

 homogeneous throughout except for occasional black blotches, some 

 of which resemble in arrangement those of moss agate, while others 

 show concentric distribution. It could not be determined without 

 sacrificing too much of the specimen, whether these were formed by 

 organic matter or by mineral matter such as oxides of iron or man- 

 ganese. The chalcedony resembles in its characters that of the 

 veins of that mineral which traverse the region and which have been 

 described by other authors.* On heating fragments of the chal- 

 cedony it turns white and opaque but yields only a trace of water. It 

 is infusible and has a hardness of 7. 



It is to the portion designated as the yolk that the greatest inter- 

 est attaches. This has already been described as a white opaque 

 ovoid mass .66 inch in diameter, enveloped in the chalcedony. On 

 close examination this white mass can be seen to be made up of two 

 portions of about equal size which have different structure. That 

 nearer the center of the egg is made up of little spherules and thin 

 curving plates. The spherules average about 1 mm. in diameter and 

 have a distinct concentric structure, coats of alternately opaque white 

 and translucent dark matter being deposited around each center. So 

 far as can be judged from the color of these coats they are opal and 

 chalcedony, respectively, but color is not, of course, in such a case, 

 an accurate criterion. The thin curving plates are similarly made up 

 of white and dark layers. 



The other portion of the "yolk" is composed of a yellowish- 



*J. B. Hatcher, Am. Naturalist, March, 1893, p. 218. E. C. Case, Am. Geologist, April, 18^5, 

 p. 248. 



