266 SUDDEN APPEARANCE OP [CHAP. X. 



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 Palaeontology, published in 1844-46 and 

 in 1853-57, the conclusions on the first appearance and disappear- 

 ance 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 occurred 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 sand- 

 stone of the United States, who would have ventured to suppose 

 that no less than at least thirty different bird-liKe animals, some 

 of gigantic size, existed during that period ? Not a fragment of 

 bone has been discovered in these beds. Not long ago, palaeonto- 

 logists maintained that the whole class of birds came suddenly 

 into existence during the eocene period ; but now we know, on the 

 authority of Professor Owen, that a bird certainly lived during the 

 deposition of the upper greensand ; and still more recently, that 

 strange bird, the Archeopteryx, with a long lizard-like tail, bearing 

 a pair of feathers on each joint, and with its wings furnished with 

 two free claws, has been discovered in the oolitic slates of Solen- 

 hofen. Hardly any recent discovery shows more forcibly than 

 this, how little we as yet know of the former inhabitants of the 

 world. 



I may give another instance, which, from having passed under 

 my own eyes, has much struck me. In a memoir on Fossil Sessile 

 Cirripedes, I stated that, from the large number of existing and 

 extinct tertiary species ; from the extraordinary abundance of the 

 individuals of many species all over the world, from the Arctic 

 regions to the equator, inhabiting various zones of depths from the 

 upper tidal limits to 50 fathoms; from the perfect manner in 

 which specimens are preserved in the oldest tertiary beds ; from 

 the ease with which even a fragment of a valve can be recognised ; 

 from all these circumstances, I inferred that, had sessile cirripedes 

 existed during the secondary periods, they would certainly have 

 been preserved and discovered ; and as not one species had then 

 been discovered in beds of this age, I concluded that this great 

 group had been suddenly developed at the commencement of the 



