242 



discovered by Dr. F. V. Haj'den in his geological explorations of the 

 Western Territories, a discovery which has justly excited a great inter- 

 est among all the paleontologists of this age. These plants represent 

 the Cretaceous flora of the Dakota group. 



This formation covers a wide area along the Missouri and Platte Kiv- 

 ers, and in Kansas, Nebraska, and Minnesota, extends from Texas to the 

 northern limits of the United States, in a width of seventy to one hun- 

 dred miles, and passes farther north into the English North American pos- 

 sessions, even apparently to Greenland. Along a portion of its eastern 

 border, as in Kansas, it overlies immediately, without any kind of transi- 

 tional strata, the Permian limestone; while near the base of the Rocky 

 Mountains it rests directly on rocks containing Jurassic fossils ; and, 

 therefore, as its animal fossils are all Cretaceous, it represents as yet the 

 lowest American Cretaceous. By the relation of some of its fossil remains, 

 however, its synchronism seems to be with the Middle Cretaceous of Eu- 

 rojie. In this formation, generally of reddish ferruginous sandy shale, 

 vegetable remains are, if not in profusion, at least tolerably abundant, and 

 especially in a tine state of preservation. They are mostly leaves, with a 

 few fruits and a few stems, from which the relation of generic types at least, 

 if not of species, is ascertainable. This Cretaceous flora, now known by 

 more than one hundred species, has not preserved any of the antecedent 

 types, not even of those of the Jurassic, the immediately preceding age. 

 The Ferns and the Conifers are few, and all represent new forms. One 

 vegetable only is doubtfully referable to Cycadw ; and, what is the more 

 remarkable, this flora mostly represents dicotyledonous plants, some of 

 them representing types of the essential genera into which our present 

 arborescent vegetation is distributed. From the Lower Cretaceous of 

 Europe, no dicotyledonous plant has been described up to the present 

 time ; one only has been recently recognized by Heer in the Old Creta- 

 ceous of Greenland, where the flora has still great affinity with that of 

 the Jurassic, especially by a preponderance of Cycafkc. It is therefore, 

 clear that the discovery of a group of plants manifesting characters re. 

 lated to those of our present flora, and found in connection with a forma 

 tion referable by its animal remains and its geological station to the Old 

 Cretaceous, should be of great interest to science. 



The monography of the fossil plants published in the reports of Di\ 

 Hayden* describes Ave species of Ferns, one doubtful Cycad, six Con- 

 ifers, three monocotyledouous, and the balance all dicotyledonous, rep- 

 resenting genera distributed in all the divisions of the present vegetable 

 scale : the apetalous, gamopetalous, and polypetalous. It is natural 

 to suppose that the limitation of species represented merely by leaves 

 cannot be very precise and accurate. But the value of the species has 

 not to be considered for the relation of this Cretaceous flora ; only the 

 typical forms characterizing genera, which may be recognized easily, 

 even by those who are scarcely acquainted with botany. The leaves of 

 the beach, for example, those of the platan or buttonwood, of the tulip- 

 tree, the sweet-gum, the poplar, the magnolia, the walnut, even those 

 of some sections of our oaks, like that of the chestnut-oak, positively 

 identify the genera which they represent. The table of the genera to 

 which the forms of the Cretaceous leaves are referable has, among 

 others, Liquidumhar, Popidus, Salix, Betula, 3Iyrica, Celtis, Quercus, 

 Ficus, Platanits, Laurus, Sassafras, Biospyros, Azalia, Magnolia, Lirio- 

 dendron, Menispcnnam, Negundo or Acer, Faliurus, Rhus, Juglans, Pru- 

 nus. From this list, seventeen of the genera are those to which belong 



' Eeport of the United States Geological Survey of the Territories. F. V. Hayden, 

 geologist-in-charge. Vol. vi. 



