;{9S The American Geologist. DecemV)er, 1897 
valleys," (p. 287). And in this connection I may cite their 
description of dunes, which may perchance prove of the same 
nature and age as those of the Peccatonica valley. 
'•The eastern bluffs along the Mississippi are frequently crowned by 
dunes of fine sand blown up from the valley below. These are usually 
composed of finer sand than is common to dunes in general, and this 
graduates almost imperceptibly into silt scarcely coarser than that of 
the loess itself: indeed not coar.ser than much loess on the face of the 
bluflfs of the Mississippi, whence, indeed the dunes seem to be partially 
derived. From these dunes there spreads backward to the east, i. e. to 
the leeward, a mantle of fine sand graduating indefinitely away into a 
deposit indistinguishable from loess proper." (Op. cit. p. 2S6.) 
The " northern drift" is a more probable original source for 
most of the loess loam of the "driftless area" than is the local 
residuary clays although both may have contributed. 
The Residuary Clay and the Glacial Phenomena. It is not 
possible as it seems to me, that the loess loam covered portion 
of the "driftless area" of Wisconsin, Minnesota and Iowa 
could have been glaciated since the deposition of the loess up- 
on it. Regarding the highest points, like the Blue mounds 
and Piatt mounds, I cannot now tell, but glaciers could not 
have been very extensive during the Wisconsin period, since 
the lowan loess mantle is ver}' extensive. Evidence of previ- 
ous glaciation must be sought under the three to six feet of 
loess loam. 
Residuary clay of the Paleozoic rocks, the same of which 
Chamberlain and Salisbury say, "the deeper-lying clay where 
limestone is the adjacent rock, is the most characteristic mem- 
ber o-f the residuary earth series" (op. cit, p. 239), is as a rule 
wanting upon sandstones even where limestone had formerly 
rested, although it is represented often by a few chert frag- 
ments, concretions or polished blocks of sandstone. This re- 
siduary clay is a structureless, dark red-brown, stilt' clay with 
irregularly intermixed fragments of chert from the disinte- 
grated limestones. It is found upon limestone, dolomite and 
clay surfaces, and reaches down into crevices or again rests 
upon frost-broken rock. It clings tenaciously on the hillsides 
and I have been surprised at times to find it thickest where I 
expected to find it eroded thin. 
At Freeport Illinois, 20 miles within the limits of northern 
drift, the same residuary clay is in i)lace in full thickness. 
