_ 1887] Mesozoic and Cenozoic of North America. 449 
marls, which lie conformably on the Niobrara beds both on the 
-flanks of the Rocky Mountains and on the northern parts of the 
Plains. Thickness (King), two hundred and fifty to three hun- 
' dred feet”? Represented in the East, according to Meek and 
Whitfield, by the lower green-sand marl of New Jersey, Dela- 
ware, etc. Invertebrate fossils very numerous; vertebrates less 
numerous in the interior basin, more so on the Atlantic slope. 
The predominant genera in the two regions are Mosasaurus and 
Elasmosaurus, the latter occurring also in the Niobrara. The 
distinctness of this horizon from the latter on grounds of verte- 
brate paleontology depends chiefly on the fauna of the Eastern 
beds. The distinctions are,— 
Presence of Reptilia Crocodilia Proccela; Pythonomorpha 
Mosasaurus.® Absence of Pisces Isospondyli Actinochiri ; Ptero- 
sauria Pteranodontidz ; Aves Odontornithes. 
It remains to be seen whether these differences will remain 
` under future investigation. 
Fox Hiits.—Formed of sandstones more or less argillaceous, 
varying in thickness from thirty feet (Cope), Montana, to fifteen 
hundred feet (King), Colorado, to three thousand to thirty-five 
hundred feet in Southwest Wyoming (King) The vertebrate 
fauna in the West is sparse, but in New Jersey it is very full. It 
is characterized in Montana by 
Presence of Pisces Holocephali * ; Haplomi (Ischyrhiza) ; Rep- 
tilia Pythonomorpha and Sauropterygia with short neck (Uro- 
nautes); 3* Crocodilia Proccela. 
In New Jersey it has the same characters, with the additions,— 
Present: Pisces Percomorphi Berycidz ; 3 Reptilia Testudinata 
ocidz and Pleurodira. Absent: Pisces Isospondyli Actino- 
chiri. 
Mr. King has combined the Benton, Niobrara, and Pierre into 
a single division, which he called the Colorado.” On palæonto- 
logical grounds there is as yet no more reason for uniting these 
without than with the Fox Hills group. If the Fox Hills is 
retained as distinct, the others should be also. However, future 
research may change the present aspect of the case. 
Total thickness of the Cretacic of the West, about four thou- 
sand nine hundred feet. 
