This occurrence was a fall of snow.
It was not late enough in the year for snow upon the lowlands, but snow falls very early in the autumn upon the summits of mountains.
Marco and Forester had not anticipated stormy weather of any kind, when they left home; for the wind was west and the sky was clear.
When, however, they had accomplished about one half of their journey, large masses of fleecy clouds began to drive over the mountains, and presently, all at once, it began to snow.

Marco was extremely delighted to see the snow falling.

Forester was not so much pleased.
On the other hand, he looked somewhat concerned.

He did not at first think how the snow could do them any serious injury, but he seemed to have an undefined sense of danger from it, and appeared uneasy.

They both, however, walked on.
The region through which the path led at the time when the snow came on, was a tract of flat land on the summit of the mountainous range, with small and scattered trees here and there upon it.