8o The American Geologist. August, i904. 
the nortlicrn crescents. Whether ia them a pushing towrnd tlie south 
has occurred can first be shown after more exact investigation. 
D. AGE OF TIClTONlC M o\ EMIC XTS. 
1 he doterniinalion of th-i age of the f.'iult structure meets a difnculty 
which influences everywhere the geological chronology of continental 
east Asia; it rests in t!:e absence of marine deposits of age' younger than 
the Triassic. The ocean sedimei.ts end for ihe most part with the 
Carboniferous. To some determinations the fresh water deposits of 
the Jurassic period give support. 
Suess* has shown in his profound work upon the asymmetry of the 
northern hemisphere, which compresses great results into small compass, 
that the pl^n of Eurasiatic folds, so far as it concerns Asiatic soil, was 
laid out in pre-C?mbrian time, the completion of its form, however, 
reaching up into Tertiary time. Tliis holds for the broader outline of 
the folding movements, but is not, however, immediately applicable to 
the fault development. 
AGE OF THE MISSOURI RIVER. 
By Warren Upham, St. Paul, Minn. 
As the sea covered the area of the Plains during the Cre- 
taceoiis period, stretching from the Gulf of Mexico north- 
ward through the United States and far into Canada, perhaps 
to the Arctic ocean, with its eastern shore crossing Iowa and 
Minnesota,! it is evident that the Missouri and Mississippi 
rivers cannot be more ancient than the Tertiary era. 
Great rivers undoubtedly flowed into this Cretaceous sea 
from the east, but we can scarcely trace their courses or out- 
Hne their basins. It seems most probable, however, that one 
of the chief river systems of that time coincided with the 
present series of the Great Lakes tributary to the St. Law- 
rence, but discharged its waters westward, opposite to the 
present direction. Another large river may have brought its 
tribute of detritus from the area of Hudson bay and the Nel- 
son river, its flow being similarly the reverse of the present 
course. 
In the region of the Ohio river many changes of drainage 
have taken place in connection with the continental glaciation, 
as made known by studies begun twenty-five }-ears ago by 
* Sitz. d. k. Akad. d. Wiss. zu Wein. Math. -Nat. CK, vol. 107, p. 94, (1900). 
t See the last preceding paper of this series, Amer. Geologist, toI. xxxiv. 
pp. 35-39,. Tuly, 1904. 
