352 UNITED STATES GEOLOGICAL SURVEY— TERTIARY FLORA. 



liave still locally persisted in deep seas. Facts of this kind are recorded in the 

 European geology. The presence of the Saurian Agathaumas in the lignite-bed 

 of Black Buttes is then certainly explainable as denoting the wandering of 

 that animal out of its domain, and its death, by penetrating into a peat-bog and 

 being irretrievably swallowed up by its soft matter. If once imbedded in sofl 

 peat, no animal, not even man, can get out of it. By this fact, and also by 

 the reason that the coriaceous, ligneous plants of the bogs are not food for 

 mammals, I explain the scarcity of bones of Eocene animals of this kind 

 in the lower beds of the Lignitic. As a shore formation, a surface covered 

 with deep bogs surrounded by sand-wastes, this primitive land would not 

 atford food to mammals, or even be accessible to them. Every one who has 

 explored peat-bogs knows how destitute these formations are of animal life. 

 Few bones of the Aurochs have been found in the bogs of North Grermany. 

 They are there quite as rare as human skeletons, and more so than implements 

 of the old races of inhabitants. And the area covered by the American 

 Lignitic shows how compact and continuous, not to say universal, were those 

 swamps of the Lower Tertiary. I believe, therefore, that if the bones of 

 Eocene mammals are not discovered in the lowest part of the Lignitic, they 

 will be found in the upper strata. Moreover, the agglomeration of bones in 

 certain localities depends on peculiar circumstances, and does not immediately 

 and forcibly relate, like plants, to the general cliaracter of a whole period. 



The land surface during the prevalence of the Lignitic formation was 

 like that of the gulf shores at the present time. A belt of sand-downs served 

 as a barrier to the sea, and extended inland, either barren or covered with 

 pine-woods, and back of it there were mostly swamps — peat-bogs, rendered 

 impenetrable by a luxuriant vegetation; everglades, like those of Florida, 

 where animal life is limited to Saurians. A formation of the same kind is 

 remarked all along the western coast of Africa, where, behind the sandy 

 beach heaped by the ocean waves, extends a dark region of woody swamps, 

 which even the inhabitants cannot penetrate — the abode of deadly fevers, of 

 snakes and crocodiles, shunned by every kind of mammals. 



The question of the subdivision of the Lignitic or Tertiary measures, 

 which I have separated into four groups, from the non-coincidence in the gen- 

 eral character of the flora, is still disputed, and this subdivision contradicted 

 by the assertion that the discordances may be merely apparent, and a result 

 of the geograjihical distribution of species, as we may see it now in groups 



