robably cross the earth's track,
while every earth-projected meteorite would necessarily do so.

If this view be true, then there must be hosts of meteorites traversing
space in elliptic orbits around the sun. These orbits have one feature
in common: they all intersect the track of the earth. It will sometimes
happen that the earth is found at this point at the moment the meteorite
is crossing; when this is the case the long travels of the little body
are at an end, and it tumbles back on the earth from which it parted so
many ages ago.

It is well to emphasise the contrast between the lunar theory of
meteorites (which we think improbable) and the terrestrial theory (which
appears to be probable). For the lunar theory it would, as we have seen,
be necessary that some of the lunar volcanoes should be still active. In
the terrestrial theory it is only necessary to suppose that the
volcanoes on the earth once possessed sufficient explosive power. No one
supposes that the volcanoes at present on the earth eject now the
fragments which are to form future meteorites; but it seems possible
that the earth may be now slowly gathering back, in these quiet times,
the fragments she ejected in an early stage of her history. Assuming,
therefore, with Tschermak, that many meteorites have had a volcanic
origin on some considerable celestial body, we are led to agree with
those who think that most probably that body is the earth.

It is interesting to notice a few circumstances which seem to
corroborate the view that many meteorites are of ancient terrestrial
origin. The most characteristic constituent of these bodies is the alloy
of iron and nickel, which is almost universally present. Sometimes, as
in the Rowton siderite, the whole object consists of little else;
sometimes this alloy is in grains distributed through the mass. When
Nordenskjoeld discovered in Greenland a mass of native iron containing
nickel, this was at once regarded as a celestial visitor. It was called
the Ovifak meteorite, and large pieces of the iron were conveyed to our
museums. There is, for instance, in the national collection a most
interesting exhibit of the Ovifak substance. Close examination shows
that this so-called meteorite lies in a bed of basalt which has been
vomited from the interior of the earth. Those who believe in the
meteoric origin of the Ovifak iron are constrained to admit that shortly
after the eruption of the basalt, and while it was stil