274 llii Ainri'KUDi Qi'dliKjist. November, 1891 
inuch greater slope of tin- <:t'iu'r:il siirfuce t li;in t lie i)reseiit. pos- 
sibly no greater. 
In .the discussion thus far tlu- uttitndt {)i the surface has hci-u 
considered and a harmonious altitude lias lieen assumed us a 
necessary factor. Abstractly it might be held that the whole 
region \vas lifted bodily witiiout disturbing its flat surface atti- 
tude, but the drainage at the edge of such a plateau, formed of 
erodable material, like that of the lower Mississippi region would 
speedily revolutionize the whole drainage phenomena and the 
topographic aspect of the valley. It is utterly incredible that the 
silts that cover the west half of the state of Mississippi were 
deposited at even thcii' present hight 1)V a stream fifty, if not a 
hundred, miles wide. No such stream could exist on the brink of 
such a plateau of soft material, or. if once formed, could main- 
tain itself for an appreciable fraction of the silt-depositing period. 
It is e(iually incredible that the broad trenches of the Mississippi 
and its tributaries could have l)een formed under plateau con- 
conditions. The whole phenomena show that low altitudes went 
with tlat attitudes. 
VII. (iritcnil ('oiicliisioiis. From this survey, which has 
necessarily been hasty and synoptical, since the details are multi- 
tudinous to the last degree. T draw the following inferences : 
First. That thioughout all the earlier stages of glaciation thus 
far determined in the Mississippi basin, the attitude of the land 
was lower and Hatter than at present and the drainage slackei-. 
Second. That during the earliest stages of what 1 have l)een ac- 
customed to interpret as the later glacial epoch, the attitude of this 
region was not far different from the present, possibly somewhat 
more elevated, and slojjing somewhat more rapidly to the south, 
but the gradient eould not have Ik'vu very considerably greater 
than the i»resent. 
Third. That thiring the inter-glaciai epcjch tlie attitude of the 
country was such as to permit erosive drainage to the depth of 
one hundred or more feet below the present flood plains of the 
leading streams. ])ut that the elevation of this period was not ex- 
cessively great is infernal from tiie fact that the trenches so cut 
were l)road as well as deep. 
Fourth. That during the closing stages of the later glacial 
epocii the attitude of the c-ountry was again flat, being toward its 
close, more depressed than at pri'sent. 
