196 THE SECONDARY AGES. 



has utterly disappeared ! But numerous as "bird-footprints 

 are an d they occur in abundance at Storeton in Cheshire, 

 Corncockle in Dumfriesshire, Cummingstone in Morayshire, 

 Hildburghausen in Germany, and on the Connecticut in 

 A-mp.rica no traces of bird-bones have been detected save 

 in a single instance, and that not altogether free from doubt, 

 in the sandstones of the Connecticut. But what is doubt- 

 ful in the Trias becomes obvious in the Oolite and Chalk, 

 and the comparatively recent discovery of the skeleton of 

 the archceopteryx * (ancient bird) in the lithographic lime- 

 stone of Solenhofen confirms the fact that Bird-Life, whether 

 existing or not in the primary periods, became at all events 

 an established feature in the secondary ages. Yet so it ever 

 appears with the great scheme of vitality ; advancing slowly 

 but incessantly, and displaying at every stage more compli- 

 cated forms and higher functional activities ! 



Conformable to this progress, mammals also make their 

 appearance during the secondary ages scantily in the 

 Trias, but more abundantly and unmistakably in the Oolite 

 and Chalk. As might be expected, and in accordance with 

 a progressional scheme, those mammals belong to the lower 

 or marsupial orders that is, to those which, like the opos- 

 sum and kangaroo, are furnished with a marsupium, or 

 external pouch in which they carry about their immature 

 young. These marsupials or pouch-bearers stand lower in 

 the scale than the true mammals that bring forth their 

 young in a perfect state. They are sometimes termed ovo- 



* This ancient bird, according to Professor Owen, was about the size of 

 a rook, and differs from all known birds in having two free claws belong- 

 ing to the wing, and also in having the vertebrae of the tail (about twenty 

 in number) free and prolonged as in mammals each vertebrae supporting 

 a pair of quill-feathers which give to the tail a long and vane-like appear- 

 ance. This unique specimen (now in the British Museum) exhibits in its 

 tail a retention of structure which is " embryonal and transitory in the 

 modern representatives of the class Aves, and consequently a closer adhe- 

 sion to the general vertebrate type." 



