204 
On the other hand, the majority of samples of what he calls 
incipient wind-blown sand, which is sand blown out of 
other deposits, have this composition, as do also his lee 
sands, which are the finer material blown beyond the body 
of a dune. 
Microscopic examination.—(1) Thin section: Three char- 
acters are conspicuous in the thin section of the original 
rock, namely, (a) its porosity, whichis evidently primary— 
that is, not produced by grinding the thin section—and 
is a character of wind-deposited material; !* (b) the angu- 
larity of most of the grains; (c) the absence of a recogniz- 
able deposit of secondary quartz on the outside of the 
grains. In many cases it can be definitely proved, by the 
presence of inclusions throughout the grain, that there is 
no outer coat of secondary quartz, and the rough angularity 
of the grains does not suggest secondary growth, which 
tends to restore crystal form, but, if anything, rather 
solution. (II) Disintegrated sand: The disintegrated 
material can be studied to greater advantage because it 
can be immersed in liquids of different indices of refrac- 
tion. Thus by immersing in a liquid of index about 1.55 
the inner structure of the quartz grains and any possible 
boundary between nucleus and secondary quartz can be 
more readily recognized. Immersing in a liquid of index 
about 1.65, on the other hand, brings out brilliantly the 
surface form and texture. Much more could be observed, 
especially in the latter liquid, than the time at my disposal 
permitted, but I can make the following generalizations: 
(a) None of the portions, not even the coarsest, reveal any 
unusual abundance of rounded grains; rather the opposite. 
(6) The surface of grains is not frosted, as is characteristic 
of wind-blown sand, nor pitted, as if subjected to much 
solution, but rather rough and chipped-looking, as might 
be the result of mechanical wear. (c) Under the favorable 
conditions afforded by immersion in a liquid of index 
about 1.55, no secondary silicification could be detected. 
(d) In the finest size a few very small well-rounded grains 
were found, the smallest having a diameter of about 0.025 
millimeter and being exceptionally perfectly rounded. 
Such a grain could probably be produced only by pro- 
longed wind action."” 
The main problem of fact, in spite of these obsetvations, 
still concerns the cause of the present form of the grains. 
Secondary silicification is often very veiled, and in the 
absence of comparative studies I am not prepared to 
commit myself as to the possibility of solution having 
acted on the grains. These two factors affect not only 
the form but also the size of the grains. However, the 
coherence of the observations made favors the belief in 
their correctness. They lead to the following conclusion: 
The portion of the Cheyenne sandstone represented by 
this sample is nothing like an eolian deposit in an arid 
region, nor even a part of a permanent dune area in a 
humid climate, but merely an accumulation of material 
blown by the wind out of a deposit of some other origin. 
Only an extensive field study could disclose the main 
accumulation from which this is separated and other 
possible associated facies and lead to a complete and 
satisfactory interpretation. From the roughness of the 
sand grains I would be inclined to assume rather a delta 
than a beach deposit as the dominant type. 
16 Goldman, M. I., op. cit., pp. 280-281. 
17 Idem, pp. 271-272. 
The very | 
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1921. 
small, perfectly rounded grain noted appears entirely out 
of place as the product of the conditions under which the 
sandstone seems likely to have been formed and must 
therefore be assumed to be the product of an earlier cycle 
in the history of the grain, unless it is assumed that in a 
deposition of secondary silica the larger grains have been 
favored so that only the smallest grains retain their 
original form; but this seems to me incompatible with 
the uniform size of the larger grains. 
As brought out in the paper on the Catahoula sandstone 
there are many more factors that might have been con- 
sidered, but being limited in time and having no assistance 
for such work I have selected the few that seemed most 
rapidly determinable and most important. 
A single sample whose position in the local 
section is unknown can be conclusive only for 
that one sample. The foreset bedding of 
which I have seen pictures suggests delta 
deposition, but no one has made field studies 
of the Cheyenne sandstone with the object of 
determining the origin of the sediments or the .. 
method of sedimentation, and Mr. Goldman’s 
report is therefore chiefly significant in indi- 
cating what definite results might be obtained 
in this region of an oscillating Cretaceous 
strand by a careful study of the problem. 
The plants and their method of occurrence 
conclusively indicate a sparse vegetation, at 
least seasonal dryness, and accumulation by 
the wind. This I am sure was a local condi- 
tion, as previously stated. Whether these 
facts do or do not indicate beaches, interstream 
sand hills, or delta deposits can be determined 
only by future studies. 
AGE OF THE FLORA. 
-Ignoring for the present the general rela- 
tions and the implications resulting from the 
age of the overlying Kiowa shale or the sup- 
posed equivalent beds in Texas, as discussed 
in the preceding section, and considering only 
the evidence of the fossil plants, I may note 
that ten of the 23 species are positively iden- 
tified as ‘‘Dakota’’ forms and two additional 
species are tentatively so identified. Four 
others are peculiar to the Cheyenne sandstone. 
The type localities of the remaining seven 
species were the Cenomanian of Bohemia (one 
species), the Atane beds of Greenland (two 
species), and the Patapsco formation of Mary- 
land (four species). 
Of the so-called Dakota forms in the Chey- 
enne flora the following species were previously 
known from only the ‘‘ Dakota”: Cladophlebis 
dakotensis (Lesquereux), Cycadeospermum line- 
