Foot-Prints. 17 



of birds, they present a singularly perfect counterpart of many 

 of the old triassic shales above described. 



Mr Darwin tells us in his " Journal of a Voyage in the 

 Beagle,'^ that the Soutli American ostriches, although they 

 live on vegetable matter, such as roots and grass, are re- 

 peatedly seen at Bahia Blanca, lat. 39° S., on the coast of 

 Buenos Ayres, coming down at low water to the extensive 

 mud-banks, which are then dry, for the sake of feeding on 

 small fish. Over such mud-flats, birds of different sizes, 

 together with alligators, turtles, and other reptiles, may 

 w£^nder and leave their foot-prints, and yet, although swarm- 

 ing by myriads, may leave none of their bones in the newly 

 deposited sediment. T have searched in vain, year after year, 

 in the shell marl of Scotland, for the evidence of the exist- 

 ence of a single bird, in a deposit made up bodily of shells of 

 the genera Lymneus, Planorbis, Succinea, and Valvata, and 

 in which the skeletons of deer, oxen, and other quadrupeds 

 are met with in considerable numbers, although we know 

 that before the lakes were drained, which yield this marl so 

 largely used in agriculture, the surface of the waters and the 

 bordering swamps were covered with wild duck and wild 

 swan, and with teal, herons, curlews, snipes, and other fowl. 

 They have left no fossil memorials behind them, because if 

 they perished on the land, their bodies decomposed or became 

 the prey of carnivorous animals ; if on the water, they were 

 buoyant and floated till they w^ere devoured by predaceous fish 

 or birds, and in warmer countries by reptiles, such as the 

 alligator. But the same causes of obliteration have no power 

 to efface the foot-prints which such creatures may have left 

 on an ancient mud-bank or shore, and these, like the ripple- 

 mark on the surface, or the casts of crevices formed by the 

 shrinkage of mud during desiccation, may be as imperishable 

 as any other portion of the solid rock. 



We have at present no fossil remains of birds in the pri- 

 mary formations of any country, and none in the secondary, 

 except the impressions, above alluded to, in the red sand- 

 stone of New England, and a few British specimens of bones 

 from the oolite of Stonesfield and the Wealden of Tilgate 

 Forest. After I had been informed by Mr Bowerbank that 



VOL. LI. NO. CI. — JULY 1851. B 



