Half an hour later, the fog had surmounted all the ridge on the opposite side of the gap, though a shoulder of the mountain still warded it out of our canyon.  Napa Valley and its bounding hills were now utterly blotted out.  The fog, sunny white in the sunshine, was pouring over into Lake County in a huge, ragged cataract, tossing treetops appearing and disappearing in the spray.  The air struck with a little chill, and set me coughing.  It smelt strong of the fog, like the smell of a washing-house, but with a shrewd tang of the sea-salt.

Had it not been for two things — the sheltering spur which answered as a dyke, and the great valley on the other side which rapidly engulfed whatever mounted — our own little platform in the canyon must have been already buried a hundred feet in salt and poisonous air.  As it was, the interest of the scene entirely occupied our minds.  We were set just out of the wind, and but just above the fog; we could listen to the voice of the one as to music on the stage; we could plunge our eyes down into the other, as into some flowing stream from over the parapet of a bridge; thus we looked on upon a strange, impetuous, silent, shifting exhibition of the powers of nature, and saw the familiar landscape changing from moment to moment like figures in a dream.

The imagination loves to trifle with what is not.  Had this been indeed the deluge, I should have felt more strongly, but the emotion would have been similar in kind.  I played with the idea as the child flees in delighted terror from the creations of his fancy.  The look of the thing helped me.  And when at last I began to flee up the mountain, it was indeed partly to escape from the raw air that kept me coughing, but it was also part in play.

As I ascended the mountainside, I came once more to overlook the upper surface of the fog; but it wore a different appearance from what I had beheld at daybreak.  For, first, the sun now fell on it from high overhead, and its surface shone and undulated like a great nor’land moor country, sheeted with untrodden morning snow.  And, next, the new level must have been a thousand or fifteen hundred feet higher than the old, so that only five or six points of all the broken country below me still stood out.  Napa Valley was now one with Sonoma on the west.  On the hither side, only a thin scattered fringe of bluffs was unsubmerged; and through all the gaps the fog was pouring over, like an ocean into the blue clear sunny country on the east.  There it was soon lost; for it fell instantly into the bottom of the valleys, following the watershed; and the hilltops in that quarter were still clear cut upon the eastern sky.