92 The American Geologist. February, i904. 
of the drainage system at a time when the Champlain epoch 
commenced, — at a time of flooded rivers. In the neighborhood 
of Lennox, however, some channels have been found, which do 
not seem to have 1)ecn connected with any of the main water- 
courses of the region, but which are rather supposed to have 
drained into the flooded bottom of the trough in the neighbor- 
hood of its axis. 
The level down to which the entire region finally subsided, 
and which may be calculated with some degree of probability 
from the present bight of the upper bowldery terraces, is sup- 
posed to have been within iSo and 200 feet below the present 
level of the Big Sioux and within 80 and 120 feet below that 
of the axis of the trough. 
'I"hc terraces, which mark tlic time of the ultimate re-eleva- 
tion of the region, the so called "Terrace' epoch, may be di- 
vided into upper and lower bowldery terraces and still lower 
terraces, on which tlic bowlders are less frequent or entirely ab- 
sent, and which on account of their being covered to some ex- 
tent at least with silt, may be called silt terraces. They have 
to some extent already been traced by J- K- Todd, while fol- 
lowing the trend of the Altamont moraine, and have been re- 
ferred to by lum in U. S. G. S. Bulletin Xo. 158, pp. 138 and 
130. The iit'fer terraces, which rise to bights from 160 to 220 
feet above the level of the Big Sioux, are to be found near Klon- 
dike on the east side of the stream at a bight of 160 feet ; a little 
farther south at even higher levels ; east of Canton at about the 
same level as near Klondike and north of Fairview about 210 
feet above the Sioux. 
Of Lower hozvldcry terraces may be mentioned one. about 
50 feet above the stream, at Klondike, on the Iowa side, another 
one east of Canton, at a level of about 40 feet, still another one, 
about two miles west of Fairview, which rises nearly 50 feet 
above the level of the stream., while a little north of Hudson, 
on the Dakota side, a terrace rises about 10 .feet higher. The 
silt terraces are met with on a far lower level, fro mio to 40 feet 
above the Mream, as for instance near Canton, where they may 
be traced with more or less distinctness. 
Attention has already been called to the terrace-like topo- 
graphy of the highlands within the southeastern corner of the 
region. TIk- highest, extending east of East Brule creek and 
