LEACHING OF DRIFT 
19 
tions, and have established two additional communieations, 
the portal vein connection and the ilio-lumbar vein connection. 
The main circulation and disposition of the lymphatic system 
has been determined and the need of further knowledge con- 
cerning the histology of the lymph nodes, of which there ap- 
pear to be two types, is pointed out. 
Laboratories of Animal Biology, 
State University op Io^a. 
LEACHING OF THE PLEISTOCENE DRIFTS OF 
EASTERN IOWA. 
MORRIS M. LEIGHTON. 
(ABSTRACT) 
The term leaching is applied by glaciologists to that process 
of dissolving and carrying out in solution by ground water the 
soluble constituents of the drift, of which lime carbonate is the 
most notable in the Mississippi Valley. This discussion of that 
phenomenon is based on observations made by the writer on 
Pleistocene deposits of the larger part of the east half of Iowa, 
and in the vicinity of Chicago, Illinois. Briefly, the evidence 
warrants the following contentions: (1) The percolation of me- 
teoric waters through clayey drifts is so slow that they become 
saturated within a few inches after the calcareous zone is en- 
countered. The zone of notable solution is, therefore, limited to 
a narrow transition zone. (2) The leaching of the drift takes 
place by the gradual deseension of this solution zone. (3) The 
rate of deseension is probably greatest from the surface down 
to the horizon of the ‘‘ground-water surface for wet seasons,” 
less rapid from this horizon down to the so-called permanent 
ground-water surface, and markedly checked at the latter hori- 
zon. (4) The bottom of the leached zone in young drifts may, 
therefore, not mark the horizon of permanent ground-water 
surface. (5) the stratigraphic horizon and topographic position 
of outcrops must be considered in quoting figures for the amount 
of leaching of a drift sheet. Other important factors are the 
amount of annual percolation of ground water, the general 
texture of materials, the size and relative quantity of calcareous 
constituents, and the amount of carbonaceous materials in the 
soil. (6) The factor of the rise of ground water into the leached 
