272 W. aS. McGee—Artificial Mounds of Northeastern Iowa. 
The occurrence of this mineral in so marked a manner in the 
Butcher meteoric irons of Cohahuila, when it does not show 
itself in the troilite of other meteoric irons, induced me to in- 
vestigate this matter carefully, as I now had chemical methods 
to aid me. us far I have examined the troilite from only 
three meteoric irons, viz., those from Toluca, Mexico; Sevier, 
Tennessee ; and Cranbourne, Australia. In the first two speci- 
was proportionally less than in the other two. The Toluca 
troilite furnished the largest quantity; the residue from 2800 
grams of it, after thorough treatment with chlorhydric acid, 
which dissolves nearly the whole of it, was dissolved in part by 
nitric acid, and on analysis the solution was found to contain 
chromium and iron representing about sixty milligrams of dau- 
bréelite; the mineral obtained from these troilites was of the 
pulverulent variety.* 
ere is reason to believe that further research will show the 
constant presence of daubréelite in meteorites. I am now 
prosecuting a series of experiments on the mineral segregations 
in meteoric irons, both those visible and invisible to the naked 
eye and those only discernible by chemical means, the results 
of which will tend to a satisfactory solution of this hypothesis. 
Art. XXXI—On the Artificial Mounds of Northeastern Iowa, 
and the evidence of the employment of a Unit of Measurement in 
their erection; by W. J. McGeExr. 
ota 
may be divided into four classes, viz: (1) tumuli; (2) conical 
imi i alle 
usually found in rows or series, and in such cases sometimes 
connected by narrow ridges; (3) embankments; and (4) animal 
mounds. Isolated mounds are sometimes found, but they occur 
much more frequently in groups; and where the topography of 
the country is favorable, many groups may be connected, form- 
ing extensive systems. All four classes of mounds often appear 
in a group, and usually in a system. When exceptions occur, 
it Is most frequently the tumuli which are found to be absent. 
Rarely an embankment or a collection of mounds is so situated 
* The undissolved portion after the nitri is princi ite 
iat < po. nitric acid treatment is principally grap: 
