Morgan and Tallmon — Occurrence of Bitumen. 365 



practically indistinguishable from the fossil shell, which shows 

 distinctly the two characteristic layers, the outer one veined, 

 the inner one prismatic. (PL XIX, figs. 2a and 2o.) The 

 shell is light buff in tint, but any inference from its present to 

 its original color would hardly be significant. It is probable 

 that when this egg was deposited the region was not near to 

 the sea. Under geographic conditions similar to those now 

 obtaining, ducks would be more numerous than any of the 

 other possible forms, and the probabilities, therefore, favor 

 anatine origin of the egg. 



Since it was not desirable to mutilate the specimen unneces- 

 sarily a quantitative analysis of the shell was not possible. 

 Qualitative analyses of the shell of the fossil egg and the shell 

 of a wild-goose's egg were made in parallel, on approximately 

 equal amounts of material in equal volumes of solution with 

 the same number of drops of the different reagents. With the 

 exception of organic matter the fossil gave tests for every 

 element found in the egg of the goose apparently to the same 

 degree, the only difference noticeable being that the fossil con- 

 tained a trifle more iron. 



Taking into consideration the facts that the fossil eggshell 

 is in chemical composition similar to, and in physical structure 

 practically indistinguishable from, the shells of birds' eggs of 

 the present time, the hypothesis that the material of the fossil 

 eggshell as it exists to-day is the same as was present origi- 

 nally seems unquestionable. Moreover, the minute tracings of 

 the shell are reproduced on the inner surface of the surround- 

 ing capsule. This fact makes it necessary to assume that the 

 egg was encased very soon after it was deposited in the nest, 

 and that subsequently it has been subjected to no conditions 

 likely to modify its microscopic structure. 



Contents. 



By far the larger portion of the contents of the egg consists 

 of beautifully crystalline colorless colemanite, showing the 

 characteristic plates, striations, cleavage, hardness, extinctions 

 and other physical properties. (PI. XIX, fig. 1.) An analysis 

 gives the following composition : 



Calculated. Found. 



CaO.._ 27-21 per cent 27*07 per cent 



B 2 3 -_ 50-93 " 51*00 " 



H.O 21-85 " 22-01 " 



While the colemanite in many places comes in direct contact 

 with the shell of the egg, in other places it is separated from 



