86 BANKS OF FOSSIL SHELLS. [CHAP. XXVI. 



clams hero in popular language, and, being thick and strong, 

 afford a good material for road-making. From the same mud- 

 bank we dug out a species of Cyrena, the only accompanying shell. 

 In some places riot far off, a Neritina is also met with. As a 

 geologist, I was much interested by observing the manner in 

 which these shells were living in the mud of the delta of the 

 Alabama River. The deposits formed by the advance of this arid 

 other deltas along the northern shores of the Gulf of Mexico, will 

 be hereafter characterized by such shells in a fossil state, just as, 

 in the Pampas, Mr. Darwin and M. A. D Orbigny found the 

 brackish-water shell, called Azara labiat.a, marking far inland 

 the position of ancient estuaries. Arid as, in South America, 

 &quot; the Pampean mud,&quot; described by Mr. Darwin,* is filled with 

 the skeletons of the extinct Megatherium, Toxodon, arid other 

 strange mammalia, so in the modern delta of the Alabama, the 

 quadrupeds now inhabiting the southern shores of the United 

 States will hereafter be met with buried in the same assemblage 

 of deposits of rnud and sand as the Gn&thodon. I was told that 

 in a great morass which we saw near the lighthouse some cattle 

 had lately perished, arid for many days the turkey buzzards have 

 been snatching parts of the dead carcasses out of the mud, watch 

 ing their opportunity the moment the dogs, which are also preying 

 on them, retire. Formerly the wolves used to prowl about these 

 swamps in search of similar booty, tearing up portions of the 

 mired cattle, arid in this manner we may expect that, while 

 sonic skeletons, which have sunk deep into the softer mud, may 

 be preserved entire, the bones of others will be scattered about 

 where the wolves have gnawed thorn, or birds of prey have picked 

 oil the flesh. 



On our way back to the town, at places a mile and a half 

 from the sea, I examined some large banks of fossil shells of the 

 G- tuitkodon, lying as if they had been washed up by the waves 

 at a time when the coast-line extended only thus far south. I 

 also found that the city of Mobile itself was built upon a similar 

 bed of shells, in which no specimens of the Neritina occurred ; 

 but I was told by Mr. Hale, that he has met with them in banks 

 * Geolog. Ohs. on S. America (1846), p. 99. 



