Geology and Natural History. 253 
three others, between the levels 22 to 38 and 64 to 73 feet; and 
varying much in depth in others. This bed is a blue delta ‘clay, 
. ‘ aie ad 
5 ae 
species of Rhizosolenia, Nitzschea, ‘Globi pili ete. e two 
have in common Orbulina universa, Melosira eet Cocconema 
lanceolatum, itera acuta, Prof. Hilgard rem 
“Stratum 8 may be a true delta deposit of she ‘present 3 Missis- 
sippi, such as €: has been since the re-elevation of the continent 
which determined the erosion of the present ep 7 of the river. 
The fact that an apparently fluviatile stratum (No. 3) occurs 
lower down, may be taken as an indication that both Nos. 2 and 
4 fall within the modern period = eye formation. Yet it is not 
e other hand, stratum No. 8 might be pei as the 
denne ola of a much thicker stratum roaaror se during the 
period of depression, ries th erefore sensibl ntemporaneous 
ceive it othe rwise than as the sean Aa of the ‘ blue-clay 
the ee bottom’ to stratum 8, speculation > to how 
“Tt wie pen m8 course, to be expected that ice ing 
eon of t elta 
lain, Yet, = pr rn as Se aero of the present investigation 
