Sqitiier—Peculiar Deposits on the Mississippi Bluffs. 265 
limestone are conspicuously shown in contrast with its own 
sandy residuum. 
We may see examples illustrating all stages from those in 
which the limestone capping of the hills displays nearly its full 
thickness, to those in which it is represented only by the last 
vanishing remnants. 
Everywhere, unless the deposits in question are exceptions, 
we find the closest correspondence between the thickness of the 
limestone cap, and the abundance of its debris in the talus. 
An an appreciable quantity the debris disappears the 
sooner. As soon moreover as any particular horizon of the 
limestone disappears from the cap, it ceases to have representa¬ 
tion in the talus, whereas the deposits in question represent at 
least a good share of its total thickness. Under ordinary con¬ 
ditions, therefore, the limestone debris as compared with the 
parent ledge is shown as relatively very ephemeral. If it ever 
shows the greater endurance it must be in certain special cases 
in which the ledge is removed with abnormal rapidity. Such 
conditions are presented by those bluffs which standing diag¬ 
onally to the river, present mural fronts at the ends where 
basal erosion is active. The example which I have chosen for 
illustration, Eig 1, is known as Queen’s Bluff. It is on the 
Minnesota side of the river, about eight miles below Trem¬ 
pealeau. It show's I think the highest vertical escarpment on 
the river. 
The cliff faces about north, while on the south side the 
slopes are normal. The recession of the cliff gives rise to pro¬ 
gressive shortening of the west end of the bluff. When in the 
future, the line of cliff shall come to occupy some position, 
e. g., a section of the lower slopes now within range of lime¬ 
stone waste, will cease to be so just as some portions now out 
of range, would have been in range when the line of cliff stood 
at say m n. If, under the conditions the limestone waste on 
the south side of the bluff persists after the disappearance of its 
parent ledge it should not only extend from a to b, with little 
apparent diminution, but beyond b toward o, gradually 
diminishing with increasing distance. The actual conditions 
