GENERAL MEETING. 97 
over southeastern Iowa; it abounds in characteristic fossils (which 
may or may not be depauperate), in loess-kindchen, and in calcare- 
ous tubes; it is fine, homogeneous, and vertically cleft; it generally 
graduates into the subjacent drift so imperceptably that neither 
geographic nor stratigraphic separation of the formations, by other 
than a purely arbitrary line, is possible; and it occurs indiscrimi- 
nately at all levels. 
So, in its distribution, the loess of eastern Iowa is intimately con- 
nected with the Driftless Region, with the drainage, and with the 
topographic configuration ; but in its disposition to seek the greatest 
altitudes in the north, and to merge into the drift in the south, its 
behavior is as anomalous as is that of the rivers of the same region. 
Mr. PowrEL. remarked that these peculiarities of drainage were 
different from those observed in the drainage systems of mountain 
regions and demanded a different explanation, which was not yet 
forthcoming. It was probable, however, that not enough allowance 
was made for the differential effects of general degradation subse- 
quent to the determination of the drainage. 
Mr. GILBERT, after defining antecedent and super-imposed drain- 
age, said that Mr. McGee’s description definitely negatived the hy- 
pothesis of antecedent drainage, and rendered the hypothesis of 
super-imposed drainage in the ordinary sense equally untenable. 
The most plausible alternative is the hypothesis suggested by Mr. 
McGee in one of his earlier papers, that the drainage was super- 
imposed by the ice-sheet, the distribution of loess having been de- 
termined at the same time and by the same causes. 
Mr. WHITE regretted that Mr. McGee’s special investigations 
did not include the portion of Iowa draining to the Missouri. The 
details of drainage in that region are equally interesting, and, in 
his opinion, do not admit of the explanation mentioned by Mr. 
Gilbert. The direction of the rivers diverges at right angles from 
that of the Mississippi tributaries, and their valleys are excavated 
from loess except along their upper courses. 
Mr. Powe 1 said that on the Illinois side of the Mississippi River 
many of the features described in the paper are repeated. The loess 
hills follow the river courses, and in the opposite directions over- 
Jook plains. The explanation of the phenomena is problematic, 
but the theory advocated by Mr. Gilbert does not appear sufficient. 
