IMPERFECTION OF GEOLOGICAL RECORD 85 



the real transitional grades through which the wings of 

 birds have passed; but what special difficulty is there in 

 believing that it might profit the modified descendants of 

 the penguin, first to become enabled to flap along the 

 surface of the sea like the logger-headed duck, and ulti- 

 mately to rise from its surface and glide through the air ? 

 I will now give a few examples to illustrate the fore- 

 going remarks, and to show how liable we are to error 

 in supposing that whole groups of species have suddenly 

 been produced. Even in so short an interval as that 

 between the first and second editions of Pictet's great 

 work on Paleontology, published in 1844-46 and in 

 1853-57, the conclusions on the first appearance and 

 disappearance of several groups of animals have been 

 considerably modified; and a third edition would require 

 still further changes. I may recall the well-known fact 

 that in geological treatises, published not many years 

 ago, mammals were always spoken of as having abruptly 

 come in at the commencement of the tertiary series. 

 And now one of the richest known accumulations of 

 fossil mammals belongs to the middle of the secondary 

 series; and true mammals have been discovered in the 

 new red sandstone at nearly the commencement of this 

 great series. Cuvier used to urge that no monkey oc- 

 curred in any tertiary stratum; but now extinct species 

 have been discovered in India, South America and in 

 Europe, as far back as the miocene stage. Had it not 

 been for the rare accident of the preservation of footsteps 

 in the new red sandstone of the United States, who would 

 have ventured to suppose that no less than at least thirty 

 ii different birdlike animals, some of gigantic size, existed 

 i during that period? Not a fragment of bone has been 



