And now all the air and the earth and the sea were shaken by a sound, low but terrible. It seemed to emanate from no special source, but to fill all space simultaneously. The lowering sky had assumed a sulfurish yellow cast. A faint wreath of vapor that overhung one of the snowcapped mountains grew suddenly dense, black, shot with forks of ruddy fire. It rolled down the mountainside, an avalanche of black cloud, and from the peak above an enormous flame burst skyward.