364 Morgan and Tallmon — Occurrence of Bitumen. 



Description. 



The egg as found forms the center of a rounded mass of 

 hard calcareous rock, which may be called the capsule or 

 matrix. Its appearance is that of an ordinary irregularly- 

 shaped river pebble, about 3^x4x5 inches in dimensions. It 

 is well worn by the action of water, and shows striations in a 

 plane parallel with the longer diameters, apparently due to 

 differential weathering of the thin layers of the matrix. By a 

 blow of a pick a piece was broken out of one side of the 

 pebble, revealing a smooth inner core, from the appearance of 

 which the finder had no hesitation in pronouncing it a fossil 

 egg embedded in rock. When the specimen came into our 

 possession, part of the surrounding matrix had been removed 

 and the egg broken open. (PL XYI1I, figs. 2 and 4.) 



In order to expose fresh surfaces for observation the matrix 

 was completely removed. It separated readily and exposed 

 what appears externally to be a typical egg in all respects. (PL 

 XVIII, fig. 1.) It is oval in shape, but little removed from an 

 ellipsoid, however, and measures 62x40 mm (2*44 x 1*57 inches). 

 Its shape indicates very clearly that it belongs to the class of 

 water-birds, and by comparison with the eggs of birds of 

 the present time, it is found to correspond closely with the 

 type of egg laid by the cormorant. The character of the 

 shell is entirely unlike these rough chalk-coated eggs, however, 

 but shows a finely pitted surface with some degree of polish 

 such as is found in eggs of the duck family. The minutest 

 markings of the shell are preserved in the matrix, moreover, 

 and in this there is no evidence of any scratches such as usually 

 occur in the chalky layer of cormorant's eggs. It is true that 

 the shell proper lying underneath the outer chalky layer of a 

 cormorant's egg shows a pitted surface much like that of the 

 present fossil specimen. It seems improbable, however, that 

 the chalky layer could have been washed off without injury 

 being done to the egg^ neither is it probable that it was firmly 

 united with the matrix and pulled away in separating the egg- 

 shell from the rock. 



While the specimen most resembles in shape the type egg 

 of the cormorant, it is also much like the egg of the larger 

 grebes or herons, the American bittern or limpkin. Again, 

 while the ratio of the short to the long diameter is somewhat 

 less than that of the typical egg of the duck, its dimensions 

 correspond almost exactly with measured eggs of many of the 

 larger species of this family, thus showing that its divergence 

 from the type is not greater than could be accounted for by 

 individual variation. 



In microscopic structure the same similarity is apparent. 

 Under the lens the shell, of a wild goose or of a duck's egg is 



