Having found a camping-place, the members of the party were at leisure to observe the nature of their surroundings; and they found themselves on the very brink of a precipice of black rock, forming the inner edge of the old crater. This wall of dark lava was mostly vertical, and the base of the cliff was separated from the snow plain beyond by a deep ditch like a huge dry moat, evidently due to the action of the blizzards. But what surprised the explorers most were the extraordinary structures which rose here and there above the surface of the snowfield. They were in the form of mounds and pinnacles of most varied and fantastic appearance, some resembling beehives, others huge ventilating cowls, while others were like isolated turrets, and yet others looked like various animals in shape. At first sight no one was able to understand the origin of these remarkable structures, but as it was time for food, they left the closer investigation until later in the day. CHAPTER XVI THE CONQUEST OF MOUNT EREBUS While some of the party cooked the meal, Marshall examined Brocklehurst's feet, as the latter stated that for some time he had lost all feeling in them. When his boots and socks were removed it was found that both his big toes were black, and that four more toes were also frost-bitten. Ultimate recovery from so severe a frost-bite was bound to be slow and tedious, though Marshall's and Mackay's efforts to restore circulation were, under the conditions, fairly successful. To climb almost continuously for nine hours with badly frost-bitten feet up the steep and difficult track must have required splendid pluck and determination. After lunch Brocklehurst was safely tucked up in the three-man sleeping-bag, and the five other members of the party started off to explore the floor of the old crater, and the mystery of those remarkable structures was soon solved by the Professor. Directing their steps towards one of the ice mounds, which bore a whimsical resemblance to a lion couchant, and from which smoke seemed to be issuing, the Professor recognised that these structures were the outward and visible signs of fumaroles. In ordinary climates a fumarole, or volcanic vapour-well, may be detected by the thin cloud of steam above it, but in the rigour of the Antarctic climate the fumaroles of Erebus have their vapour turned into ice as soon as it reaches the surface of the snow-plain. Thus ice mounds, somewhat similar in shape to the sinter mounds formed by the geysers of New Zealand, Iceland and Yellowstone Park, are built up round the orifices of the fumaroles of Erebus. Next morning when the party got up at 4 A.M. they had a splendid view of the shadow of Erebus projected on the field of cumulus cloud below them by the rising sun, and while Marshall was attending to Brocklehurst, the hypsometer, which had become frozen on the way up, was thawed out, and a determination of the boiling-point made.