ough its own greater gravity slowly displacing the lighter air in
the lower strata? I do not know, but I am inclined to accept the latter
explanation. I do know that it travelled at the rate of about six miles
an hour; and its coming was observed somewhat in detail by two other
observers besides myself--two people who lived twenty-five miles apart,
one to the north, one to the south of where I hit it. Neither one was as
much interested in things meteorological as I am, but both were struck
by the unusual density of the fog, and while one saw it coming from the
north, the other one saw it approaching from the south.

I have no doubt that at last it began to mingle with the clearer air and
to thin out; in fact, I have good testimony to that effect. And early
next morning it was blown by a wind like an ordinary fog-cloud all over
Portage Plains.

I also know that further north, at my home, for instance, it had the
smell of the smoke which could not have proceeded from anywhere but the
marsh; and the marsh lay to the south of it. That seemed to prove that
actually the mist was spreading from a common centre in at least two
directions. These points, which I gathered later, strongly confirmed my
own observations, which will be set down further on. It must, then,
have been formed as a layer of a very considerable height, to be able to
spread over so many square miles.

As I said, I was reminded of those mist pools in the north when I
approached the cliff of the fog, especially of that "waterfall" of mist
of which I spoke. But besides the difference in composition--the fog,
as we shall see, was not homogeneous, this being the cause of its
wetness--there was another important point of distinction. For, while
the mist of the pools is of the whitest white, this fog showed from the
outside and in the mass--the single wreaths seemed white enough--rather
the colour of that "wet, unbleached linen" of which Burroughs speaks in
connection with rain-clouds.

Now, as soon as I was well engulfed in the fog, I had a few surprises.
I could no longer see the road ahead; I could not see the fence along
which I had been driving; I saw the horses' rumps, but I did not see
their heads. I bent forward over the dashboard: I could not even see
the ground below It was a series of negatives. I stopped the horses. I
listened--then looked at my watch. The stillness of the grave enveloped
me. It was a little past five o'clock. The silence was oppressi