FLORA OF THE CHEYENNE SANDSTONE OF KANSAS. 
Lesquereux described is the same as that 
described by Richardson” in 1915 as the 
Purgatoire formation and referred to the top 
of the Lower Cretaceous. This formation has 
also frequently been called “Lower Dakota.”’ 
Below this, in the type section at Morrison and 
within the Morrison formation (“ Atlanto- 
saurus beds’’) as originally described, there is 
about 100 feet of friable sandstone and shale 
containing traces of a flora similar to that 
found in the overlying sandstone. This flora 
has been discussed by Knowlton," who quite 
rightly concludes that it is Upper Cretaceous. 
I am not concerned in this paper with the 
taxonomic proposals regarding what shall be 
the stratigraphic limits of the Dakota, but 
solely with the general relations and their bear- 
ing on the geologic history of the region and 
the boundary between Lower and Upper 
Cretaceous. 
It has been customary for geologists, par- 
ticularly those who had a leaning toward 
philosophy, to postulate a rhythm of positive 
and negative movements of the strand by 
which the boundaries of the different systems 
could readily be determined. There may be 
some physical basis for this conception, but it 
should be recalled that all series of changes can 
be considered rhythmic, with some elasticity 
in the application of criteria, and I am one of 
those reactionaries who believe that, however 
imperfect the scheme as devised for the region 
first and longest studied, namely, Europe, the 
classic names and approximate limits of the 
‘systems should be adhered to; for, after all, the 
best classifications, whether of geologic time 
or of formations, igneous rocks, or organisms, 
are those which are most easily understood and 
used. 
Time is continuous, time boundaries are 
always subjective, and the time-honored 
terms Permian or Triassic or ‘‘ Lower Carbon- 
iferous” or Lower Cretaceous are to me as 
essential to clear thinking and the interchange 
of geologic ideas among nations as the minutes, 
hours, and days of the current time scheme, 
however illogical these may seem in sidereal 
astronomy. 
According to the customary American 
scheme the Lower Cretaceous should be con- 
12 Richardson, G. B., U.S. Geol. Survey Geol. Atlas, Castle Rock folio 
(No. 198), 1915. 
13 Knowlton, F. H., Am. Jour. Sci., 4th ser., vol. 49, pp. 189-194, 1920. 
201 
sidered to have ended with the withdrawal of 
the Lower Cretaceous sea and the Upper 
Cretaceous to have begun with the initial 
transgression of the Upper Cretaceous sea. 
Where the interval between these two events 
was ‘long, with continental deposition, much 
confusion and difference of interpretation re- 
sults. A classic instance of such differences 
is the controversy over the boundary between 
the Cretaceous and Tertiary in the Great 
Plains and Rocky Mountain region of North 
| America, which the Tertiary sea was so incon- 
siderate as not to invade. If geology at its 
inception had concerned itself chiefly with 
continental deposits and land plants and ani- 
mals and had ignored marine formations and 
life the situation would be exactly reversed, 
and the marine sediments would probably be 
those in dispute. 
On none of the continents, so far as I can 
discover, did the sea complete a cycle of inva- 
sion and withdrawal of what might be called 
the first magnitude during the Lower Creta- 
ceous epoch. In the Atlantic Coastal Plain 
no marine Upper Cretaceous deposits. earlier 
than the European Turonian are known ex- 
cept in the Texas area, where marine forma- 
tions representing a part but not all of the 
Lower Cretaceous of -Europe advance halt- 
ingly from the south. The oldest of these 
formations is the Trinity, which in my judg- 
ment is nowhere as old as the Neocomian of 
Europe. This is followed by the Fredericks- 
burg group, which Hill called Neocomian but 
which contains a younger fauna. If one dis- 
regards Bése’s correlations of the Mexican 
Cretaceous on the ground that Mexico is too 
remote from the north Texas-Kansas area, 
Whitney’s studies of the fauna of the Buda 
limestone not only clearly show its Cenomanian 
age but also show that it is late Cenomanian. 
Similarly the fauna of the Georgetown lime- 
stone is Cenomanian. (Whitney has refrained 
thus far from making any intercontinental 
correlations.) It is a striking confirmation 
of this correlation that the Buda limestone 
near Austin and hence in the region of more 
continuous marine conditions than farther 
north should be immediately overlain by the 
Turonian Eagle Ford formation. The problem 
of working out the interfingering of forma- 
tions between north and central Texas is 
largely a problem of invertebrate paleontology 
