On Fossils from the Potsdam of Wisconsin, etc. [227] 3 
sisting entirely of bluish or iron-stained quartzite, exhibiting a 
gradual passage into an overlying conglomerate, which, in turn, 
assumes, above, the characteristics of the Potsdam sandstone. 
Both insist on the absolute continuity and conformability of the 
quartzite, conglomerate and sandstone. Mr. Wood says: “It 
is in the northern slope of the main ridge (on the east of the 
lake) that I found these fossils. If the sandstone containing 
them shall be called ‘Potsdam,’ and the main ridge ‘Quartzite,’ 
then I should say that they were a continuous deposit; and I 
do not know of any reason for separating them, only that they 
differ in hardness; while it is only at the extremes of the scale 
that this difference is manifest.” Prof. Hall states (Geol. Rep. 
Wis. 1862, pp. 11 and 12) that the quartzite is terminated up¬ 
ward by a conglomerate which graduates into the Potsdam 
sandstone; and agrees with Mr. Wood, that “in some cases the 
passage from the conglomerate to the sandstone is so gradual 
that it is impossible to point out a line of* demarcation. In the 
lower part,” Prof. Hall further says, “ the conglomerate is so des¬ 
titute of any other materials than the sand and pebbles of the 
quartzite below, that it bears little affinity to the sandstone 
above.” Nevertheless Prof. Hall is of the opinion that “the 
quartzite holds the same relative position to the Potsdam sand¬ 
stone as the Huronian system of the Canada survey.” 
Some of the fossiliferous fragments forwarded by Mr. Wood 
contain pebbles three-fourths of an inch in diameter; and I 
should infer from this circumstance, as well as the position 6f 
the fossils upon the northeastern flanks of the bluff, that the 
remains under consideration occupied a place near the boundary 
line between the conglomerate and the recognized Potsdam 
sandstone. 
I insist particularly upon the strati graphical position of these 
fossils, because they show, contrary to the conclusions of Prof. 
Hall’s monograph, that Dicellocephalus and Ptychaspis occur at 
the recognized base of the Potsdam sandstone, as well as above. 
The alternative of this conclusion is an admission that the con¬ 
glomerate and quartzite are truly {as they appear to he) the down - 
ward continuation of the Potsdam sandstone , and the prolongation 
of beds which, further north, exhibit a more typical character. 
If, as I infer from Mr. Wood’s communications, the mass of 
quartzite is superimposed, a little further south, by the outliers 
of the Calciferous sandrock, this fact would give countenance to 
the alternative suggested. 
ScOLITHUS LINEARIS. 
S. linearis Hall, is present in abundance in some of the frag¬ 
ments, in the form of straight, cylindrical, nest-like cavities, two 
or three inches long, extending vertically to the planes of bed¬ 
ding. They vary from *05 to -27 of an inch in diameter. 
