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                    Pie Corals of Delafeld.                185
              THE CORALS OF DELAFIELD.
                         BY IRA M. BUEL.
  The large collection of fossils made by the Geological Survey
at Roberts' quarry, Delafield, Wisconsin, is surpassed in interest
and scientific value by no other representation of Palaeozoiu
fauna ever obtained from our state. It contains thousands of
specimens almost perfectly preserved by the blue friable shale in
which they were imbedded; and of the seventy species already
distinguished, about one-half are new to science. The coralline
representatives found here are of special interest to the student
and naturalist.
  The locality in question (Sec. 2t, T. 7, 1R. 18 W.) lies on the
southern shore of Pewaukee lake, and in the edge of a trough
carved by glacial forces out of the lower layers of the Niagara
limestone, and the soft underlying Cincinnati shales; the basin
being occupied in part by the lake itself. By the removal of the
limestone layers in the quarry, quite a surface of this shale was
exposed, and as this formation somewhat resembles some of the
Carboniferous shales, it was supposed by some inquiring mind to
belong to that formation. A shaft was accordingly sunk at this
point for the discovery of coal, and was not abandoned until a
depth of fifty feet had been reached. The mound of rock and
clay thrown out of this pit or shaft, the rain-washed monument of
a geological delusion, was the source of all of the specimens ob-
tained from that locality.
  These corialline forms are all of small size, the smallest species
measuring about an inch in length and about a tenth of an inch
in diameter. The largest coral fragment is about two inches in
diameter and consists of a sort of central base from which a num-
ber of slender arms branched out. Within these limits we find
almost every possible variation in form, manner of growth, branch-
ing and surface markings.
  The size, form and arrangement of cells and cell walls, are the
principal distinguishing features of these corals ; and as these feat-
ures are mainly microscopic, the labor of identification of species
and varieties among these thousands of specimens was not a small