troxell: fossil birds eggs 



423 



Fig. 1. Fossil egg, first specimen, 

 view, about natural size. 



Exterior 



FIRST SPECIMEN 



The first specimen (length 59 mm., diameter 43 mm.) has the 

 shell intact except at a few spots where it has been eroded away. 

 Immediately beneath the shell is a layer of chalcedony about 



2 mm. thick, continuous, 

 though slightly irregular 

 on its inner surface. 

 The first half shows no 

 banding but is a homog- 

 enous layer of transpar- 

 ent material deposited 

 from the colloidal silica 

 within, while the inner 

 half, resulting from an 

 intermittent or periodic 

 deposition which soon 

 ceased, shows the band- 

 ing peculiar to agate. 

 Within, the egg is filled with calcite, except for a small sili- 

 ceous geode at one end; thus the calcite was formed after the 

 outer layer of agate was in place. The diverse lines of cleavage 

 show that the calcite is 

 not a single crystal, al- 

 though it now fills the 

 cavity completely. 



There must have been 

 a hollow in the calcite 

 at the smaller end of the 

 egg which is now occu- 

 pied by the irregular 

 mass of chalcedony, for 

 the outer surface of the 

 latter, with its flat faces, 



sharp angles, and irregU- Fig. 2. Same, sawed in two and polished. 



lar Striations, indicates About natural size. Note the band of agate 

 ,, , ., -, i next to the shell, the chalcedony geode at the 



tnat it came alter and smaller end> and the c i eavage p i anes G f the 



fashioned itself to the calcite crystals. 



