LOWER CRETACEOUS FORMATIONS AND FAUNAS 601 
in northern Chihuahua it reaches 4000 feet, as estimated by Dr. 
C. A. White,’ and still farther south very much greater thick- 
nesses have been reported. Lithologically the Comanche series 
as a whole contrasts strongly with the Cretaceous rocks of all 
other parts of the United States, and indeed of North America, 
excepting Mexico, which is directly connected with the Texan 
area. Judging from the descriptions, lithologically similar Cre- 
taceous rocks are developed to some extent in the northern part 
of South America and in southern Europe. We must go to these 
regions also, and especially to Portugal and Spain, as Mr. Hill 
has pointed out, to find closely related faunas. 
Fossil plants have been obtained from two horizons, one in 
the Glen Rose beds of the Trinity division, about 250 feet above 
the base of the series, and the other in the so-called Cheyenne 
sandstone, at the base of the Cretaceous section in southern 
Kansas, but apparently within the Washita division. The 
plants from the lower horizon, which are directly associated with 
an abundant marine fauna, have been described by Professor 
Fontaine. He recognized twenty-three distinct forms, consist- 
ing mainly of conifers and cycads, with a fern, an Equisetum, 
and a few forms of uncertain affinities. Of these seven are rep- 
resented by identical and six by similar species in the Potomac, 
four occur in the Wealden of Europe, two in the Urgonian, with 
an additional one represented by a similar form, and six are 
peculiar to the Glen Rose. In discussing the age and affinities 
of these plants Professor Fontaine says: ‘‘The plants found at 
Glen Rose show, so far as can be judged from so imperfect a 
collection, that the Trinity flora finds its closest resemblance in 
the older portion of the lower Potomac. There is, however, this 
important difference: no trace of angiosperms, even the most 
archaic, has been found in the Texan region, We have only the 
four elements of the typical Jurassic flora. This, then, makes the 
Trinity flora somewhat older than that of the oldest Potomac. 
The absence of angiosperms and the presence of the forms that 
* Am. Jour. Sci., 3d ser., Vol. XX XVIII, 1889, pp. 440-445. 
?Proc. U.S. Nat. Museum, Vol. XVI, 1893, pp. 261-282. 
