I could neither see any clouds of smoke, although I gazed steadily at the mountain for hours, and could from my post survey it far down the sides.
As we descended we found the snow melting at a depth of 500 to 600 feet; lower down, the whole mountain smoked, which I thought was the consequence of the returning warmth of the sun, for my thermometer now stood at nine degrees of heat.

I have noticed the same circumstance often on unvolcanic mountains.

The spots from which the smoke rose were also cold.
The smooth jet-black, bright, and dense lava is only found on the mountain itself and in its immediate vicinity.

But all lava is not the same: there is jagged, glassy, and porous lava; the former is black, and so is the sand which covers one side of Hecla.

The farther the lava and sand are from the mountain, the more they lose this blackness, and their colour plays into iron-colour and even into light-grey; but the lighter-coloured lava generally retains the brightness and smoothness of the black lava.
After a troublesome descent, having spent twelve hours on this excursion, we arrived safely at Salsun; and I was on the point of returning to my lodging, somewhat annoyed at the prospect of spending another night in such a hole, when my guide surprised me agreeably by the proposition to return to Struvellir at once.