LOWER CRETACEOUS FORMATIONS AND FAUNAS 583 
now customary to recognize only two principal divisions — Lower 
Cretaceous and Upper Cretaceous — instead of three as formerly. 
The number and nomenclature of the subdivisions varies in dif- 
ferent countries and with different authors, but the terms Neoco- 
mian, Urgonian, Aptian, Albian, Cenomanian, Turonian, Senonian 
and Danian proposed by d’Orbigny are frequently used and 
universally understood. 
In Neumayr’s Erdgeschichte* the following arrangement is 
adopted: 
Upper Cretaceous. Lower Cretaceous. 
Senonian. Gault. 
Turonian. Aptian. 
Cenomanian. Neocomian. 
In this classification of the Lower Cretaceous the Wealden 
is treated as simply a non-marine facies of the Neocomian, 
the Urgonian is made a subdivision of the Neocomian (as 
it was by d’Orbigny also) and the English name Gault is sub- 
stituted for Albian. Some authors place the Gault in the Upper 
Cretaceous, but for comparison with American formations it is 
more satisfactory to classify it with the older beds. 
These minor subdivisions are not applicable to the American 
Cretaceous excepting in the most general way, and, as Dr. 
White has insisted, it is not probable even that the correspond- 
ing principal divisions as recognized on the two continents are 
strictly homotaxial, but the accumulating evidence tends to show 
that the difference is not very great. In making an independent 
and natural classification of our formations we have perhaps 
placed a few beds in the Lower Cretaceous that by European 
standards would go in the Upper Cretaceous. 
The first definite recognition of Lower Cretaceous in this 
country based on good evidence was by Professor Jules Marcou,? 
who in 1855 identified a number of fossils from Texas as Neoco- 
mian, and asserted that rocks of that age cover considerable 
* Bd. 2, p. 344. 
? Pacific R. R. Reports, 8vo edition, Vol. IV, pp. 40-48, 1855; republished in 4to 
edition and in Geology of North America. 
