654 
by external than internal forces, is reduced to 
sand. | 
It is doubtless true that a part of the vol- 
canic sand and dust results from the tritura- 
tion of solid material in the process of violent 
eruption; but, at the same time, it is generally 
believed that by far the largest portion of the 
latter is produced directly by the distention 
and explosion of multitudinous vesicles in the 
amorphous, viscous portion of the magma, and 
is the extreme product of the same operation 
which produces pumice. Mr. I. C. Russell has 
recently. described some interesting volcanic 
dust from the Great Basin of Nevada. It 
has been traced two hundred miles from its 
source, the Mono craters, and has about the 
same chemical composition as the glassy lava 
of that place. This can be readily understood 
when we consider, that, at the time of its erup- 
tion, the magma contained few, if any, well-de- 
veloped crystals. The difference in chemical 
composition between volcanic sand or dust, and 
the lava to which it belongs, appears to be di- 
rectly proportional to the amount of crystalli- 
zation which has taken place in the magma 
before its effusion. The composition of the 
Unalashka sand is such as to indicate that be- 
fore its eruption there were many crystals 
secreted in the magma, so that there would 
be a proportionally small amount of siliceous 
dust produced. While it is evident that the 
constitution of volcanic sand is very variable 
from place to place, yet it is such in this case 
as to clearly indicate that it came from a cra- 
ter erupting hornblende andesite, and that its 
basic character may be explained by suppos- 
ing that the siliceous portion of the magma 
was carried away in the form of dust. The 
unaltered condition of the minerals and ground- 
mass indicates that the sand has not been 
exposed to atmospheric influences for any 
considerable length of time, and favors the 
opinion of Mr. Applegate, that the sand came 
from the new crater, near the Island of Bogos- 
loff, about sixty miles to the westward. 
The precipitation of volcanic dust has been 
reported from several places in the United 
States, but it is all of very questionable de- 
termination. Mr. G. P. Merrill, of the U.S. 
national museum, has recently investigated 
that which fell at Rome, N.Y., and proved it 
to be an ordinary dust, composed chiefly of 
minute fragments of quartz and iron-stained 
products of decomposition. All of the re- 
ported dusts, of which I have been able to 
obtain samples, have been found to be like 
that which is most common about dusty cities 
and plains. A little experience will readily 
SCIENCE. 
enable one to distinguish the Pélé’s-hair and 
glass globules, in the dust of blast-furnaces 
and other iron-works, from the glass particles 
in volcanic dust. ; 
The origin and distribution of the uncommon 
forms of dust are beginning to receive the at- 
tention they deserve; and it is a matter of 
gratulation, that the signal-service of this coun- 
try has already taken steps towards systematic 
observations upon this subject at several ele- 
vated stations, such as Mount Washington and 
Pike’s Peak, as well as in Alaska. 
U.S. geological survey. | Jo.) ieee 
METEOROLOGICAL CHARTS OF THE 
NORTH ATILANAEG: 
ONE cannot fail, in studying the progress of mari- 
time meteorology, to be impressed with the value 
placed on the Maury charts, as evinced by the fre- 
quency, with which they have been copied, or have | 
served as the basis for more extended work in foreign 
countries. But it is also to benoticed, that in recent 
years the tendency has been towards more originality 
and independence in the work of the several nations 
that take part in this branch of physical investiga- 
tion; and, further, that while Maury’s principle of 
exhibiting as far as possible the separate observa- 
tions on which averages are based is retained, his plan 
of dividing charts according to topics has been re- 
placed by the much more practical division according 
to time. The masterof a vessel, beginning a voyage 
in May, does not care to find on his chart informa- 
tion about the winds of all the year, but prefers in- 
formation of all kinds about May, and especially about 
the winds, calms, gales, squalls, and fogs of that 
month. 
Having considered, in a previous article, the de- 
velopment of maritime meteorology as shown in the 
wind-charts of the North Atlantic, published by 
various foreign governments since Maury’s time, it 
is with satisfaction that we can now turn to a work 
on the Atlantic, executed in our own country, in 
which the advance from the earlier styles of charting 
is as well marked as in any of the examples given 
above. 
On the charts whose title is given in the note,! we 
find the atmospheric conditions over a large area 
shown with greater detail, and based on a larger 
series of observations, than in any other charts yet 
published. The number of observations is extraor- 
dinary. The chart for March alone has wind-obser- 
vations for 211,057 hours. That part of the chart 
which corresponds to the six of Toynbee’s ten-degree 
squares north of the equator has 63,846 hours: the 
1 Meteorological charts of the North Atlantic Ocean for the 
months of March, April, and May. Published June, 1883, at the 
hydrographic office, Washington, D.C. J.C. P. Dekraft, com- 
modore, U.S.N., hydrographer to the bureau of navigation. 
Prepared under the supervision of Lieut. Joon H. Moors, U.8.N. 
Charts for June and July were published in March and April, 
1884. T.R. Bartlett, commander, U.S.N., hydrographer. 
