1878. ] . Recent Literature. 245 
division, and perhaps his second division, is of mesozoic and cre- 
taceous type; and also that that of the Wasatch (or Green river) 
epoch, or Prof. Lesquereux’s fourth group, lower division, is of 
Eocene Tertiary age. The evidence in favor of these positions 
has been steadily accumulating since I first announced them in 
1869 and 1872, no exceptions have come under my notice, and 
their applicability has been extended to all parts of the North 
American continent which have yet been explored. In fact the 
most important interruption in the vertebrate life of North 
America is found between the Laramie and Wasatch epochs, and 
there only can the line between the Cretaceous and Tertiary 
periods of this continent be drawn. 
The evidence in favor of this position has been in a measure 
overlooked by Prof. Lesquereux. He remarks (p. 30): “ As no 
kind of cretaceous animal remains have been discovered in the 
Lignite of Colorado, none either in that of the north, generally 
called the Fort Union group, the question of age essentially bears 
upon that Bitter Creek series. The line of demarkation between. 
the cretaceous and the tertiary is placed by Prof. Cope above the 
Black Buttes Saurian Bed.” ` The facts as regards.the amount of 
vertebrate evidence in favor of the cretaceous age of the Laramie, 
are as follows: In 1869 I determined the vertebrate remains from 
the Fort Union beds of Dakota, which had been supposed to be 
mammalian, to be reptilian, and indicative of the Mesozoic char- 
acter of the Fort Union beds of the Missouri. The number of 
rof. Lesquereux seeks t : 
saurian Agathaumas sylvestre in a bed of Tertiary plants as did Prof. 
See Bulletin U. S. Geological Survey Territories. III, No. 3, 1877- 
