^60 The American Geologist. April, isns 
Tertiary time. The resulting trenches can be recognized in many 
parts of the elevated region. The rivers of the middle Atlantic slope 
have cut trenches one, two or three hundred feet below the Tertiary 
base-level. The young narrow gorges of the upper Ohio and its 
branches cut into the earlier widely opened and mature valle3'S, de- 
scribed in Bulletin 58 of the Geological Surve}' by Chamberlain, are 
probabl}' of the same date as the trenches of the rivers flowing into 
the Atlantic. The trench of the lower Mississippi as well as the 
trench of the upper Mississippi and the narrow vallej'S of the 
rivers which trench the Tertiary- lowland of the driftless area of 
Wisconsin appear to be also of the same date. 
This minor cycle can be recognized only along the larger rivers 
and along the lower courses of their tributaries. Remote from the 
main drainage lines and where Tertiary erosion had not reduced 
the river channels to base-level, the effect of elevation was simply 
to accelerate the rate of down-cutting: it was not expressed in any 
topographic feature of the valle3's. 
The attempt will not be made to carr}' the histor}' of the devel- 
opment of the Mississippi drainage bej'ond the point which has 
now been reached. The interesting and complicated effects of the 
ice invasion, which must be considered as but an accident in the 
Tertiary cj'cle of development, if touched on at all would form 
so large a chapter that the}* cannot be embraced in the present 
discussion. 
THE CORRECT SUCCESSION OF THE OZARK 
SERIES. 
By G. C. Broadhead, State University, Columbia, Mo. 
The va]"ious members of the Ozark series, as described, de- 
fined and numbered in the earl}' geological reports of Missouri, b}- 
Swallow, Shumard and others, have been referred to frequently 
since bj' others, and the harmony and correctness of the earlier 
geologists have been acquiesced in by the later workers. In Jul}', 
1891. the writer defined and briefly" described ' 'The Ozark Series. " 
I have also called attention to the fact, notably in the article just 
referred to, that the Ozark series seemed, both by fossils and lith- 
ologic characters, to be naturally separated from the Silurian 
above, and should probably be referred to the Cambrian, especially 
the terranes lying below the first sandstone, and the strata of more 
