American and English Fossil Floras. 493 



contrary, seeming to be closely allied to well-developed types, which 

 we had been accustomed to consider distinctive of a late stage in 

 the Tertiary. It is now matter of history that Heer, to whom 

 specimens were sent, identified them as of Miocene age, and that 

 two celebrated European geologists, Professors Marcou and Capellini, 

 proceeded to America, and as a result of their examination of the 

 plant-beds of Nebraska, fully endorsed Dr. Hayden's view as to 

 their Cretaceous age. 



In order to make my subject intelligible, it is necessary to first 

 notice the salient characteristics of the Cretaceo-Eocene series in 

 America ; but as I know nothing concerning them that has not been 

 published, I will do so as briefly as possible. The bibliography is 

 very large, and it would be impossible in a few lines, and with my 

 insufficient study, to attempt any minute accuracy, but I believe a 

 general statement to be sufficient for the purpose, and approximately 

 correct. 



The formation is very vast, certainly 15,000 to possibly 20,000 

 feet in thickness, and extending north and south from New Mexico 

 to far into the British possessions. The sedimentation throughout 

 the entire series, though interrupted locally, seems to have been 

 practically continuous, as reported from the first by Dr. Hayden, and 

 is universally admitted to be of Cretaceous age at the bottom, and of 

 late Tertiary age at the top. 



The " Loioer Cretaceous " of America. — The lowest stage, or one 

 of the lowest, is that called Dakota, which appears to be from 500 

 to 700 feet thick, and consists of alternating coloured clays and 

 sandstones, with seams of impure lignite and silicified wood. The 

 deposits are marine, brackish and freshwater, mostly deposited in 

 very shallow water, or even between tides. The raoUusca are 

 chiefly bivalve, but Ammonites, Belemnites, ScapJdtes, Baculites, 

 and Inoceramus are met with, together with prints of bird and 

 saurian tracks, ripple-marks, cracks, the impress of rain and hail, 

 and occasionally bones of reptiles. Associated with these are leaves 

 of the higher types of dicotyledons. With the Dakota formation 

 are grouped the Colorado, Fort Benton, Niobrara, and other groups, 

 raising the total thickness to over 2000 feet, the entire mass being 

 usually considered in America to represent the period of the Gault, 

 Upper Greensand, or Grey Chalk of Europe. 



The " Upper Cretaceous " of America. — The next group has been 

 called " Upper Cretaceous," and consists of the Fox Hill, Fort 

 Pierre, and other local subdivisions, whose aggregate thickness seems 

 to be some 1000 to 2000 feet. Baculites, Scaphites, and BeJemnitella 

 are still present, but are mixed, especially in the Fox Hill group, 

 with Gasteropods, whose facies is entirely Eocene. The whole 

 series is considered by American and most other geologists to be 

 equivalent to the Upper White Chalk and the Maestricht beds. All 

 the formations, whether from California, New Mexico, New Jersey, 

 Mississippi, Nebraska, Alabama, or elsewhere, of Cretaceous age, are 

 grouped in either the upper or lower of these formations. 



The "Post-Cretaceous" Series of America. — This is also known 



