troxell: fossil birds eggs 



425 



The flattening and consequent increase in circumference 

 caused a series of perpendicular cracks around the edge, just 

 such as might be formed by flattening a mud ball. Although 

 fracturing occurred, the pressure within was sufficient to pre- 

 vent the entrance of clay or other solid material. It is quite 

 probable, therefore, that the egg was fresh when buried and that 

 the surrounding mud, after settling, solidified before the removal 

 of the animal matter and before the deposition of calcite began. 



Fig. 5. Same as figures 3 and 4, showing the crystalline interior. About 

 natural size. The large amber crystal of calcite in the center seems to have taken 

 the place of the yolk, while the white crystals surround it. This similarity is 

 only an interesting coincidence, for the parts, except the shell, bear no relation 

 to the original egg. 



Calcite is the only mineral occupying the cavity of this speci- 

 men; beneath the shell there is a 5 mm. layer made up of small 

 crystals and within this, occupying the center but not entirely 

 filling it, is a large double crystal of amber hue. One is struck 

 at once with the great similarity in appearance to a modern 

 egg in which are found the shell, white, and yolk in the same 

 position and relative proportions. It is an unusual case of 

 mimicry on the part of inanimate nature, for it is incredible 

 that the soft part of an egg should exert such an influence on 

 crystallizing calcite as to impose its form and color. 



