130 EARTH FEATURES AND THEIR MEANING 



feet below the summit of the cone (Fig. 132 a), and by early after- 

 noon the cone-destroying stage began with the rise of a dark " cauli- 

 flower cloud " or pino to replace the lighter colored steam cloud. 

 The cone was beginning to fall into the crater, and old lava debris 

 was mingled in the ejections with the lava clots blown from the 

 still fluid material within the chimney. From now on short and 

 snappy lightning flashes played about the black cloud, giving out 

 a sharp staccato " tack-a-tack." The volume and density of the 

 cloud and the intensity of the crater explosions continued to in- 

 crease until the culmination on April 7. On April 5 at midnight a 



FIG. 131. Scoriaceous lava encroaching upon the tracks of the Vesuviaii railway 

 (after a photograph by Sommer) . 



new lava mouth appeared upon the same fissure which had opened 

 near the summit, but now some 300 feet lower (Fig. 132 &). The 

 lava now welled out in larger volume corresponding to its greater 

 head, and the stream which for ten months had been flowing from 

 the highest outlet upon the cone now ceased to flow. The next 

 morning, April 6, at about 8 o'clock, lava broke out at several 

 points some distance east of the opening 6, and evidently upon 

 another fissure transverse to the first (Fig. 132 c). The lava sur- 

 face within the chimney must still have remained near its old 

 level, effective draining had not yet begun, since early upon 

 the following morning a small outflow began nearly at the" top of 

 the cone upon the opposite side and at least a thousand feet higher. 



