SCIENCE. 
209 
ered who have passed beyond tribal society to national so- 
ciety based on property, i.e . , that form of society which is 
characteristic of civilization. Some peoples may not have 
reached kinship society ; none have passed it. 
Nations with civilized institutions, art with palaces, 
monotheism as the worship of the Great Spirit, all vanish 
from the priscan condition of North America in the light of 
anthropologic research. 
Tribes,- with the social institutions of kinship, art with 
its highest architectural development exhibited in the struc- 
ture of communal dwellings, and polytheism in the worship 
of mythic animals and nature-gods, remain. 
THE GENESIS OF CERTAIN IRON ORES.* 
Bv Dr. T. Sterry Hunt, LL. D., F.R.S. 
Dr. Hunt began by considering the presence of iron, gener- 
ally in a ferrous condition, in mineral silicates, in the crys- 
talline rocks, and its liberation therefrom by the sub-mrial 
decay of these as hydrous ferric oxide. This, as is well 
known, is, bj' the agency of organic matter, again reduced 
to ferrous oxide, which is dissolved in natural waters by 
carbonic acid or some organic acid, from which solutions 
it may be deposited either as hydrous peroxide (limonite, 
etc.,) as carbonate (siderite), as silicate, or as sulphide 
(pyrite, etc.), in all of which forms iron is found in sedi- 
mentary deposits. As regards the formation of siderite, he 
described experiments which show that solutions holding 
five grammes of ferrous carbonate dissolved as di-carbonate 
in a litre of water, are spontaneously decomposed in close 
vessels at the ordinary temperature, and deposit two-thirds 
of their iron as a white crystalline (hydrated) mono-carbon- 
ate, with liberation of carbonic-dioxide. This serves to 
render more intelligible the reduction and segregation of 
iron as siderite in earthy sediments, as long since pointed 
out by W. B. Rogers, for the ores of the coal-measures. 
The intervention of soluble sulphates, and their reduc- 
tion through organic agency to sulphides, determines the 
formation of sulphide of iron in sediments. The genera- 
tion of a bi-sulphide (pyrite or marcasite) was then dis- 
cussed, and it was shown that the ferrous mono-sulphide, 
which naturally is first generated, may fix a further portion 
of sulphur and thus form a more stable compound. One 
■example of this is seen when recently precipitated hydrous 
ferrous sulphide is brought in contact with a solution of a 
ferric salt, which takes up a portion of the iron, leaving 
sulphur free to unite with the undecomposed sulphide, and 
form therewith a very stable higher sulphide of iron. Ex- 
periments now in progress lead the writer to believe that 
sulphur liberated from soluble sulphides may, in a similar 
manner, unite with ferrous sulphide, and thus help us to 
explain the generation of pyrites in nature, in the presence 
of water, at ordinary temperatures. 
The changes of siderite and pyrite under atmospheric in- 
fluences were next considered. The latter by oxidation 
yields, as is well known, ferrous sulphate. Its frequent 
conversion by sub-aerial decay into limonite was conceived 
to be due to the intervention of water, holding carbonates, 
which, conjointly with oxygen, changes it into hydrous 
peroxide (limonite), which often retains the form of the 
pyrites. The transformation of carbonate of iron into 
hydrous peroxide is a familiar fact. 
Limonite ores may thus be produced in three ways. 
They are sometimes formed by the peroxidation and preci- 
pitation of dissolved ferrous salts, as in the so-called bog- 
ores ; but more frequently' from the alteration in situ of de- 
posits of pyrite or of siderite. Such are the limonites 
which mark the outcrops of beds or veins of pyrites in the 
decayed crystalline rocks of the Blue Ridge. The similar 
ores found in the decaj'ed Taconic schists of the great Ap- 
palachian valley can be shown to be due in some cases to 
the alteration of included pyritous masses, and in others to 
the alteration of similar masses of siderite, both of which 
are found in the unaltered Taconic rocks, as, indeed, at 
various other horizons in the geological series. 
If we take the specific gravity of pyrites at 5.0, we shall 
find that its complete conversion into a limonite of sp. gr. 
* Read before the A. A. A. S., Boston, 1880. 
4.0 would be attended with a contraction of only' 2.7 hun- 
dredths, while if the limonite have a sp. gr. of 3.6, there 
would be an augmentation of 10.7 p. c. With siderite of 
sp. gr. 3.6, on the contrary', its conversion into limonite of 
the same density' would result in a contraction of 19.5 p. c., 
and into lemonite of sp. gr. 4.0 to a contraction of 27.5 p. c. 
The evidences of this contraction may be seen in the struc- 
ture of the limonite derived from siderite. The process 
operates from the surface of the masses, often resulting in 
the production of geodes. Their structure will generally 
serve to distinguish the sideritic from the pyritic limonites. 
These differences were illustrated in the history of various 
iron ores in the Appalachian valley', and it was further 
pointed out that the pyritic limonites, other circumstances 
being equal, should be freer from phosphorus than those 
derived from siderite, since the native carbonates almost 
always contain phosphates, from which pyritous deposits 
are comparatively free. The source of limonites thus be- 
comes a question of importance to the metallurgist. In 
conclusion it wus pointed out that deposits of manganese 
ores are, in some cases at least, generated by' the alteration 
in situ of manganous carbonates, by a process analogous 
to that by which limonite is produced from siderite. — 
MICROSCOPY. 
NEW CELL FOR OPAQUE OBJECTS. 
I desire to call the attention of the microscopists and 
preparers of objects generally to the new rubber cell for 
opaque slides, recently devised by me. A considerable 
experience in mounting opaque slides during the past few 
years has convinced me that much of the labor incident to 
it could be avoided, if a cell of suitable material and shape 
could be produced at a nominal cost. This, I think, has 
now been attained, and I take pleasure in submitting one 
lor which I claim convenience, cheapness, and general 
utility. With it the amateur can produce a slide fully as 
perfect, and with as great a degree of neatness as can the 
professional. The cell is of hard rubber, highly polished, 
and of attractive shape ; the base is solid, thus giving a 
black back-ground of rubber ; around the top is a ledge 
fitted to receive a one-half inch cover glass ; this, being 
secured by a little shellac or any similar cement, com- 
pletes the mounting. The cell may be attached to a glass 
slip by any cement, before or alter preparation. For ex- 
changes it offers superior advantages, inasmuch as the cell, 
with objects enclosed, may be sent through the mails in- 
dependent of the glass slips, the recipient attaching them. 
In this way a saving is made in postage, and no risk of loss 
by slips being broken in transit. 
They will solve the problem which often perplexes the 
student or collector who is crowded for cabinet room. 
Many objects lor future reference may be mounted in this 
simple cell, numbered and put away without a slide, a 
cabinet drawer holding two hundred of them, while but 
forty slides could be accomodated in the same space. 
The above sectional view conveys a good idea of its 
shape, the dotted line indicating the position of the thin 
glass cover. 
1 have made arrangements to have them supplied by the 
following firms at thirty cents per dozen, five cents extra 
on single dozens to cover cost of postage and box, and they 
may be obtained from the parties mentioned below or from 
the subscriber. In remitting small sums three cent postage 
samps may be used. 
Geo. S. Woolman, No. 116 Fulton St., New York ; Jas. 
W. Queen & Co., Chestnut St., Philadelphia; Bausch & 
Dransfield, Arcade, Rochester, N. Y. ; W. H. Bullock, 
No. 126 So. Clark St., Chicago, Ills. 
In conclusion I would add that I have had these rubber 
cells prepared without regard to any pecuniary gain to 
myself, hoping they may prove an aid to those engaged in 
microscopical research. 
H. F. Atwood, 
No. 50 Hamilton Place, Rochester, N. Y. 
[We have seen a sample of Mr. Atwood’s rubber cell, 
and consider it a very perfect arrangement for opaque 
objects. — E d.] 
