oat 
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R, D. Irving—St. Peters and Potsdam Sandstones. 409 
from nearly white, through gray, pink and purple to purplish- 
red, and even brick-red. Now and then a tendency to an are- 
naceous texture is observable, and occasionally small areas are 
little more than moderately indurated sandstone. It is from 
one of these least indurated portions that the present specimen 
is taken. The rock is only a little more indurated than that 
above described as from the Pots- 
dam of Black River Falls. The 4 i 
interference has been too great to 
allow the formation of any crystal- e 
line outlines in the deposited quartz. nd 
The rock is, however, much further from a true quartzite than 
either of those above described from the St. Peter’s sandstone. 
Figures 8 and 9 represent grains broken from this rock. 
_ The sandstone thus described grades immediately into a more 
indurated rock, A specimen taken a few inches rom it shows 
a rock much like that of the St. Peter’s at Gibraltar Bluff, both 
as to texture and amount of induration; and this resemblance 
f deposited quartz 
The only dis- 
ii a 
vi 
YH th fis 
Within a few inches from the point at which the specimen 
