The Súla river, or Núpsvatn, had to be crossed. It was deeper than I had before seen it, though its volume of water scarcely seemed to have increased. Its bed was changed to one of pebbles and quicksand. In 1871 it was of pebbles only, in 1874 it was black sand, in 1875 it is again pebbles and sand.
We crossed the river and fast sped on our way over the desert of Skeiðarár Sandr. This sand occupies an area of 300 square miles. It has been formed by the joint efforts of volcanoes upon the Vatna and Mount Örœfa, which have strewn this tract with sand and ashes, and whose ejectamenta have been brought down by the shifting waters of numerous glacial streams which traverse the Skeiðarár Sandr in many directions. It would seem that the portion of the Vatna which here bounds the Skeiðarár Sandr upon the north has acted in a similar manner to the Breiðamerkr Jökull; for numerous _moraines_ occur upon these sands, some of which are at a great distance from the utmost limit of the Jökull at the present time. Indeed, there has been an obvious advance at this point since 1871 of the fringe of the glacier which almost surrounds the Vatna Jökull. The existence of scratched rocks in _moraines_ in Iceland below the limit of the glaciers does not of necessity prove that such glaciers have bodily advanced, as during extensive eruptions of glacial mountains huge masses of ice frequently slip forward to considerable distances, scratching the harder and furrowing the softer rocks in their progress, which, upon their melting, leave large piles of glacial _débris_, in no way distinguishable from a _moraine_ stranded upon the lower elevations.
It was blowing hard from the east with heavy rain, but upon the west side of the mountain before us (Örœfa) the sun was shining in the most tantalising manner, so that as we urged our horses along the heavy sands we were fain to fancy ourselves exploring those dazzling glaciers and snowy slopes which seemed to fascinate the sunshine and detain it from reaching us.
We were soon under the lee of the mountains before us. Sheltered from the wind and the storm, we could stop to admire the grand sweep from the Örœfa to the commencement of the Skeiðará Jökull. Looking back at Núpstað, we saw it enwrapped in gloom, the clouds clustering round the Lómagnúpar,[1] a mountain which seems to attract all the bad weather to Núpstað and the storm sat heavily upon the western portion of the plain of Skeiðarár Sandr, which was exposed to the fury of the east winds.