A FOSSIL EGG FROM SOUTH DAKOTA. 



The specimen (Museum No. P 5734) described in this paper is 

 believed by the author to be a petrified egg of an Anatine bird of 

 Early Miocene age. If this supposition be correct, the specimen 

 seems to warrant description both as an interesting case of petrifac- 

 tion and as indicating the presence of aquatic birds about the waters 

 of the great lake which is generally considered to have occupied 

 in early Tertiary times the region where the specimen was found. 

 The original finder of the specimen was Mr. Kelly Robinson of 

 Dakota City, South Dakota. He stated to the writer that while 

 riding one day in the summer of 1896 in the region of the Bad 

 Lands he saw this object lying at the foot of "a bad land"* and 

 in a shallow gully. It had apparently washed there from "the bad 

 land " above. Mr. Robinson picked it up and concluding, on exami- 

 nation, that it was a petrified egg, took it home for a curiosity. 

 From him it was obtained by the writer for the Museum in the 

 winter of 1897. The specimen is not quite completely ovoid in form 

 since from one end a portion has been broken away. Mr. Robinson 

 stated that this portion was missing when he found the specimen. 

 The form of the specimen is fully indicated by Figs. 1, 2 and 3, PI. 

 XX, where are shown photographs of it in three different positions. 

 As may be seen from these figures, the resemblance of the specimen 

 both in form and structure to an egg is very striking. Covering most 

 of the exterior is a thin, black layer .017 of an inch in thickness 

 which closely resembles in thickness and appearance an egg shell. 

 Within this and constituting the major portion of the specimen, is a 

 mass of pale gray translucent chalcedony, corresponding in appear- 

 ance and amount to the white of air egg. Near one side but enveloped 

 in the preceding is a white, opaque, ovoid mass .66 of an inch in diam- 

 eter which can be easily seen to correspond in size and position to 

 the yolk. If the specimen be not a petrified egg, therefore, it is as 

 perfect an imitation of one in external appearance as can be con- 

 ceived of. 



In order to determine the existence of any special characters in 

 the mineral matter of the specimen this was studied somewhat in 



* In modern Western parlance M a bad land " is any knoll or slope barren of vegetation. 



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