^"'.'q^^^'] Shvfuldt, Fossil Birds' Eggs. 87 



form of this egg, when whole, was typically ovate, and the 

 external surface of the shell roughish and granular. Apparently, 

 it was originally crushed in the manner above stated — that is, 

 from side to side. This allowed its contents to escape completely 

 and rapidly, their place being taken by the mud or whatever it 

 was of that nature which subsequently fossilized. It would 

 further appear that when this egg was crushed, the fracture 

 admitted of one large piece coming away, sooner or later. This 

 was on one side, and extended up to and included a part of the 

 apical end of the egg. Nearly all this area is very rough, pre- 

 senting many irregular, confluent elevations and depressions that 

 render it so. 



When this specimen is held with the shell-side towards one, 

 the apex pointing upward, there will be noted, on the right-hand 

 side, well above the butt or big end of the egg, a place where the 

 internal fossilized material bulges outwards, presenting a limited, 

 fiat, superior surface, evidently cut off by the sharp edge of the 

 shell above it. This is well seen in fig. 2 of Plate I., where, by the 

 high light upon it, it has reproduced white. Now, that must 

 have happened after the egg was filled with the mud or other 

 substance which subsequently fossilized, and before the process 

 of fossilization had rendered it so hard, firm, and implastic that 

 it would have been impossible. Still holding the egg in the above 

 position, it will be noted, on the side away from the observer and 

 continuous with the place above described, that there is a longish, 

 longitudinal, and somewhat extensive area where the fossilized 

 shell subsequently came away. Beyond any manner of doubt, 

 then, this egg was subjected to some considerable pressure both 

 before and ajfter the process of fossilization was complete, though 

 after its interior had been completely filled with the mud that 

 found its way in there. Further, it would appear that this 

 crushed egg rested on the muddy area where it settled down, and 

 where its interior was filled. As fossilization proceeded, and its 

 matrix being continuous with the same material that filled its 

 interior — that is, the mud — the process was simultaneous within 

 and without the shell. Later on pressure was exerted, the 

 specimen flattened, and eventually was broken loose from the 

 general semi-fossilized matrix. This will account for the very 

 rough surface on the side where the shell is gone and where the 

 mud entered. That this is now somewhat ivorn is evidence that 

 the wearing took place after the specimen was detached from its 

 matrix and became a free agent. No thin, rough, calcareous 

 coating or envelope was ever deposited on the shell of this 

 fossil bird's egg, such as is often seen in the case of other speci- 

 mens. 



From this point on it is difficult to trace the career of this fossil 

 egg. When Mr. Gidley discovered it, it formed the apex of a 

 small pinnacle of the Oligocene clays, which are so much a feature 

 of the terres maiivais ("Bad Lands") of Southern Dakota. At 

 some time or other these clays were horizontally disposed ; but 



