As a rule the agglomerate is a tumultuous, unstratified mass. But in many places it shows lines of bedding and, as already stated, passes outward into ordinary bedded tuff, the number and size of the ejected blocks rapidly diminishing. Where this transition occurs we seem to see a remnant of the base of the actual volcanic cone. Thus, in the most westerly vent already cited, while the wall of the vent has been laid bare on the side next the sea, so that the agglomerate on the beach descends vertically through the surrounding bedded tuffs, on the western side the cliffs have preserved a portion of the material that accumulated outside the orifice (Fig. 187). In this section we observe that the coarse agglomerate which fills up the main part of the vent has been left with a hummocky, uneven surface, and that a subsequent and perhaps feebler eruption of finer material has covered over these inequalities, and has extended to the left above the fine tuffs through which the agglomerate has been drilled. [Illustration: Fig. 187.--Section of part of a volcanic neck on shore to the south-east of Poyll Vaaish Bay, Isle of Man.] [Illustration: Fig. 188.--Section of successive discharges and disturbances within a volcanic vent. Scarlet Point, Isle of Man.] Again, in the largest of the vents, that near Scarlet Point, still clearer proof of successive eruptions and dislocations within a volcanic chimney may be noticed. At one point the accompanying section (Fig. 188) has been laid bare by the waves. The oldest accumulation is a fine green granular tuff (_a_), rudely and faintly arranged in layers inclined at high angles, like the fine materials in many of the vents of the basin of the Firth of Forth. This peculiar stratification, due not to the assortment of materials in water, but to the deposition of coarser and finer detritus by successive explosions, and to subsequent slipping or tilting, is a characteristic feature of the detritus which has filled up ancient volcanic funnels. A later explosion from some adjacent part of the same vent has given rise to the discharge of a coarse agglomerate (_b_), which with blocks sometimes six feet long, overspreads the earlier material. A third detrital accumulation in the same vent, consisting of a firm brecciated tuff (_c_) with much calcite in its matrix, has been brought down by a slip (_f_) which cuts across both of the previous deposits. A broad dyke (_d_) of vesicular diabase (augite-porphyry) traverses the vent, and is probably later than any of the other rocks in the section.