Ch. XVI] EOCENE STRATA IN THE UNITED STATES. 



Fi<>\ 274. Fig. 2T5. 



311 



Zeuglodon cetoides, Owen. 

 Basilosaurus, Harlan. 



Fi2. 274. Molar tooth, natural size. 



Fig. 275. Vertebra, reduced. 



double occipital condyles only met with in mammals, and the convo- 

 luted tympanic bones which are characteristic of cetaceans. 



Near the junction of No. 2 and the incumbent limestone, No. 8, 

 next to be mentioned, are strata characterized by the following shells : 

 Spondylus dumosus [Plagiostoma dumosum, Morton), Pecten Poul- 

 soni, Pecten perplanus, and Ostrea cretacea. 



No. 3 (fig. 273) is a white limestone, for the most part made up of 

 the Orbitoides of D'Orbigny before mentioned (p. 309), formerly sup- 

 posed to be a nummulite, and called iV. Mantelli, mixed with a few 

 lunulites, some small corals, and shells.* The origin, therefore, of 

 this cream-colored soft stone, like that of our white chalk, which it 

 much resembles, is, I believe, due to the decomposition of these 

 foraminifera. The surface of the country where it prevails is some- 

 times marked by the absence of wood, like our chalk downs, or is 

 covered exclusively by the Junijwrus Virginiana, as certain chalk dis- 

 tricts in England by the yew tree and juniper. 



Some of the shells of this limestone are common to the Claiborne 

 beds, but many of them are peculiar. 



It will be seen in the section (fig. 273, p. 310) that the strata Nos. 

 1, 2, 3 are, for the most part, overlaid by a dense formation of sand 

 or clay without fossils. In some points of the bluff or cliff of the 

 Alabama River, at Claiborne, the beds Nos. 1, 2 are exposed nearly 

 from top to bottom, whereas at other points the newer formation, No. 

 4, occupies the face of nearly the whole cliff. The age of this over- 

 lying mass has not yet been determined, as it has hitherto proved 

 destitute of organic remains. 



The burr-stone strata of the Southern States contain so many 

 fossils agreeing with those of Claiborne, that it doubtless belongs to 

 the same part of the Eocene group, though I was not fortunate 

 enough to see the relations of the two deposits in a continuous sec- 



* Lyell, Quart. Journ. Geol. Soc, 1847, vol. iv. p. II 



