FEBRUARY 23, 1912] 
tent of pre-Glacial oxidation. (6) Evidence of 
small amount of oxidation since the Wisconsin 
epoch. (7) Evidence that the till of the earlier 
Glacial epoch consists largely of material oxidized 
during pre-Glacial times. (8) Evidence of unoxi- 
dized material mingled with the highly oxidized 
material of the earlier epoch. (9) Evidence indi- 
cates that the date of the Wisconsin epoch is to be 
reckoned by thousands, rather than by tens of 
thousands of years, and the earlier epochs by tens 
of thousands rather than by hundreds of thousands 
of years. 
The paper was discussed by F. Leverett, J. W. 
Spencer, H. L. Fairchild and the author. 
The Intermingling of Pleistocene Formations: B. 
SHIMEK. 
The paper discussed the effect produced by ice- 
sheets passing over older Pleistocene formations. 
Special illustrations are found in the mingling of 
fossiliferous loess and Wisconsin drift at Des 
Moines, Iowa, fossiliferous silts at Sioux Falls, 
S. D., and in other places. 
Loess a Lithological Term: B. SHIMEK. 
The term ‘‘loess’’?’ has commonly been under- 
stood as implying a more or less distinct division 
of time. The fact is set forth that there are sev- 
eral loesses deposited at different periods and that 
loess does not designate a distinct period of time, 
but indicates rather a condition of deposition, as 
do such terms as ‘‘sandstone,’’ ‘‘limestone’’ and 
OG Ghee? 
Professor Shimek’s two papers were discussed 
by W. C. Alden, F. V. Emerson, Frank Leverett, 
G. F. Wright and the author. 
Criteria for the Recognition of Ancient Delta 
Deposits: JOSEPH BARRELL. 
Previous to the discussion of eriteria, definitions 
were given and an analysis of the parts of a delta. 
The criteria naturally are different for each part. 
Variations in the proportions of the parts, the 
ratios in which these may enter into ancient for- 
mations and the intergradations of parts were next 
considered. Where the conditions of delta growth 
were such as to give gradations between parts, the 
criteria become overlapped and tend to result in 
confusion. It is concluded that deltas of previous 
geologic ages have commonly developed under quite 
different conditions from those taken as typical in 
modern deltas. The principle of a delta cycle is 
next developed, showing the theoretic stages of 
rivers building outward and upward against the 
sea, followed in a later stage by marine dominance 
SCIENCE 
317 
and plantation. Where the larger features of an 
ancient deposit are known, the principle of the 
delta cycle may be of value as a criterion of origin. 
Illustration is made by application to the late 
Mesozoic formations of the Atlantic Coastal Plain. 
The evaluation of stratigraphic criteria is next 
taken up with the view first of separating the sub- 
aerial delta beds—those periodically exposed to 
the air, from the subaqueous—those permanently 
covered with water. Secondly, however, the cri- 
teria record also physiographic and climatic 
conditions controlling the character of the beds. 
The stratigraphic criteria are taken up in order, 
and the degree of significance attaching to each 
is discussed. Two chief conclusions are reached. 
First, the need of extended study of the strati- 
graphie characters of present sedimentation. 
Second, most individual criteria are to some de- 
gree indeterminate and a conclusion in regard to 
the mode of origin of a formation or part of a 
formation should, in order to obtain acceptance, 
be based on the convergence of several lines of 
evidence. 
Stratigraphic and Paleontologic Features of An- 
cient Delta Deposits: A. W. GRABAU. 
After a brief reference to the pre-Cambric or 
early Cambrie delta fan of the Pacific Province 
and the Torridon of Scotland, the author discussed 
the late Ordovicie and early Silurie fans of the 
Appalachian region, the Schawangunk dry delta 
fan and its relationship to the Salina desert, the 
Esopus delta and its relation to the Oriskany de- 
posits, the Early Devonic talus breccia of Mich- 
igan and western Ontario, the Old Red of Scotland 
and the Catskill group, the Pocono, Mauch Chunk 
and Pottsville and the Triassic fans of America 
and western Europe, with special reference to 
their stratigraphic and paleontologie characters 
and their bearing on paleogeography. 
A Mississippian Delta in the Northern New River 
District of Virginia: E. B. BRANSON. 
A delta started in the Devonian in the New 
River district and continued through most of the 
Mississippian. The thickness of the Mississippian 
part is more than 5,000 feet and consists of vari- 
colored shales and sandstones that thin out in all 
directions excepting southeast from this region. 
The Mississippian rocks are known as the Pulaski 
formation and are to be correlated with the Pul- 
aski, Greenbrier, Bluefield and Hinton formations 
fifteen miles farther north. 
Discussion of the last three papers was partici- 
pated in by J. M. Clarke, David White, G. W. 
