374 Morgan and Tallmon — Occurrence of Bitumen. 



external source, and have been deposited as it now is inside 

 the eggshell. 



Evidence of an adequate source for the tar in the limestone 

 in which the fossil was embedded seems to be entirely want- 

 ing. There is no bituminous matter in the matrix, neither is 

 there an appreciable quantity of any pyrobituminous material. 

 Moreover, the ready decomposability of the tar with the forma- 

 tion of a product insoluble in petroleum ether indicates clearly 

 that the temperature of its surroundings could never have been 

 as high as 150° C. But at this temperature there was no evi- 

 dence at all of pyrobituminous material, since the small amount 

 of gas produced was liberated only at a red heat. 



Considering the indubitable evidence that the tar was pre- 

 sent before the colemanite came in, the small amount of bitu- 

 minous matter present inside the shell, rather than an egg tilled 

 full of the material, is not without its significance. 



Considering the highly fragile nature of an egg and the 

 perfect state of its preservation, the conclusion that it was 

 encased very soon after it was laid seems inevitable. This 

 must mean the inclusion of its natural contents. 



There is no reason to suppose that the egg of any previ- 

 ously existent bird, the shell of which is so similar to present 

 daj r specimens as to be indistinguishable even under the 

 microscope, would differ materially in the chemical nature of 

 its contents. 



In the eggs of the various families of birds which have 

 been analyzed, there is but a slight variation in the relative 

 proportions of the constituents, a difference not sufficient to 

 invalidate the present considerations. The average composi- 

 tion of the edible portion of ducks' or geese's eggs may be 

 taken as 15-5 per cent protein and 14'5 per cent fat. Very 

 probably these figures closely represent the composition of 

 water birds' eggs as a whole. The cubical contents of the 

 fossil egg is 49 ccm . Assuming the specific gravity of its 

 natural contents to have been 1 (it is usually a trine greater), 

 there would be about 7"5 grams of fat and somewhat more of 

 dry protein. Assuming that the protein would lose all of its 

 nitrogen and sulphur as ammonia and hydrogen sulphide or 

 their equivalents, and that part of its carbon would disappear 

 as the .monoxide or dioxide or their equivalents, 40 per cent 

 of the dry weight of protein would still remain if these decom- 

 positions took place without the intervention of oxygen from 

 without. Under the same circumstances more than 90 

 per cent of the fat would still remain. There is, of course, 

 the probability of a decomposition resulting in the formation 

 of methane, but of the magnitude of this reaction no infer- 

 ences can be drawn or allowances made. The assumption of 



