CAUSES OF PRESERVATION. 157 



fresh-water shells, linmea, planorbis, palludina, valvata, and cyclas imbedded 

 in green clay. ( Vide Appendix H.) 



Sir Charles Lyell has observed the disposition of Mastodon relics in a 

 great number of localities in the United States from North to South, and has 

 come to the conclusion, as said by him in the " Annals of Natural History," 

 vol. xii. p. 126, that these deposits are later than those of the drift and 

 boulder; but that, "although the date of the imbedding of these mam- 

 malian fossil remains is so extremely modern, considered geologically, it 

 is impossible to say how many thousand years may not have elapsed since 

 the Mastodon and other lost species became extinct." 



Although the facts in our possession do not warrant any exact division 

 of the geological localities of Mastodon Giganteus, we find . some reason to 

 distinguish them into deep or ancient, and superficial or modern ; the former 

 having occurred before the present geological condition, the latter since. 



Of the former we' may adduce the following, some of which have already 

 been mentioned, viz. : — 



TERTIARY. 



1. " It is now clear that they existed anterior to the upper tertiary in 

 this country, and that they belonged to the medial tertiary or older pliocene 

 period." — F. A. Conrad: Fossils of the Medial Tertiary of the U. States, p. 10. 



2. "The loam [with which these bones are found] rests, at Vicksburg 

 and other places, on eocene or lower tertiary strata." — C. Lyell : Report on 

 the Delta and Alluvial Deposits of the Mississippi, before the British Associa- 

 tion at Southampton, 1846. 



3. " Sixty feet deep near the mouth of the Wabash in Ohio ; also skin 

 and hair in digging a w T ell." — De Blainville: Osteographie, p. 340. 



