370 GEOLOGICAL SURVEY OF THE TERRITORIES. 



number of genera and species have been indicated by Professor Agas- 

 siz, as follows : Ecliinorliinus Blakei, Scymnus occidentalis, Galeocerdo 

 productus, Frionodon antiquus, Hemipristis heteropleurus, Carcharodon 

 rectus, Oxyrhina plana, Oxyrhina tumula, Lamna clavata, Lamna ornata. 



BATIDES. 



The skates are indicated in the Ocoya Creek tertiary by the frag- 

 ment of a tooth referred by Professor Agassiz to the genus Zygobates. 



ONCOBATIS. 



An extinct genus of rays is indicated by an osseous scale of peculiar 

 character, from the tertiary deposit of Castle Creek, Idaho. 



Oncobatis pentagonus. 



The scale upon which the species is founded was discovered in asso- 

 ciation with abundance of remains of cyprinoid fishes, and is interesting 

 as indicating most probably a large form which inhabited fresh water. 



V.— ON THE FOSSIL PLANTS OF THE CRETACE- 

 OUS AND TERTIARY FORMATIONS OF KANSAS 

 AND NEBRASKA. 



By L. Lesquereux. 



CHAPTER I. 



ON THE MODE OF PRESERVATION OF THE FOSSIL PLANTS, AND ON THE 

 CIRCUMSTANCES UNDER WHICH THEIR FOSSIL1ZATION HAS BEEN EF- 

 FECTED. 



Eesearches for fossil plants are, in this country, so rarely undertaken 

 under a scientific direction, that their discovery is mostly a matter of 

 chance, giving rise to speculations and queries of a most extraordinary 

 kind. Not only our flexuous stems of Stigmaria have been often con- 

 sidered as snakes of a prodigious size,, but many times in my explora- 

 tions I have been amused by preposterous questions like this one, ad- 

 dressed to me by people, who, recognizing a branch of fern upon a speci- 

 men of shale of the coal, wished me to explain " by what means plants 

 of such slender size could pierce the stones and grow into them." It is 

 not, therefore, inopportune to say a few words on the questions heading 

 this chapter. 



Every kind of woody tissue, when shut out of atmospheric influence, 

 (or of oxidation,) either by water or by any other matter, escapes de- 

 composition for an indefinite length of. time. In such circumstances, the 

 wood is subjected to a slow kind of combustion, of which the first state 

 is a softening of the tissue or of the whole mass. Timber used as piling 

 in water or in clay is found, after centuries, blackened, and more or less 

 plastic, without any trace of decay. Whole forests of the pliocene age 

 have been imbedded in clay, or submerged, and the trees have now their 

 tissues as soft as the clay itself, though their structure is in a perfect 

 state of preservation. It is the same with some deposits of lignites of 

 the tertiary, which are a mere compound of heaped trunks of trees whose 

 wood has become black as coal, but is still soft as clay. This first 



