VI KIOMBO 93 



carrying porphyritic plagioclase. The interspaces then became 

 partially filled with the finer fragments of the glass and of the 

 crushed felspar ; but they were in the main occupied by a still 

 liquid magma which penetrated into the cracks of the glass- 

 fragments and into those of the felspars, where the fractured 

 portions in some cases remained in position. There it has become 

 devitrified and often palagonitised. Whether this liquid magma 

 was produced by a partial remelting resulting from the heat de- 

 veloped during the crushing of the glassy upper portion of the 

 flow during the contracting process, or whether it was squeezed 

 upwards from the less consolidated lower portion, I cannot deter- 

 mine, although the last supposition seems more probable. At all 

 events the edges of the glass-fragments are peculiarly eroded as if 

 by the magma. (The bearing of these facts on the origin of 

 palagonite is discussed in Chapter XXIV.) 



I infer that this flow has descended from the hills west of 

 Kiombo. Huge masses of agglomerate are exposed in the lower 

 third of the hill marked " 470 feet " in the chart, and immediately 

 north of the town. Fine clayey tuffs are exposed in the hill at the 

 back and to the westward of this place ; but the locality requires 

 a more detailed examination. The absence to all appearance of 

 vesicular and scoriaceous rocks in the case of this basaltic flow is 

 remarkable. This would not have been expected in the case of a 

 supra-marine flow ; and indeed the testimony of the tuffs of this 

 peninsula sufficiently indicates that during their deposition the 

 whole district was submerged. 



The future inquirer will doubtless discover some old volcanic 

 " necks " in the hills of this peninsula. One such hill overlooks 

 the Soni-soni inlet about a mile west of Kiombo. It is a singular 

 isolated hill which I have named Bare-poll Peak for descriptive 

 purposes. In my notes its height is stated as 120 feet, but it 

 appeared to me to be rather higher than this. It is capped by two 

 huge masses, 14 or 15 feet high, of a dark grey slightly scoriaceous 

 augite-andesite with a cryptocrystalline groundmass, which ap- 

 parently form the uppermost portion of a volcanic " neck " or pipe. 

 According to the size of these rock-masses the " neck " would have 

 a circumference of 80 or 90 feet. These masses are in part incrusted 

 with agglomerate. 



The adjacent island of Soni-soni, which is almost joined by the 

 mangrove-belt to the adjoining coast, probably represents one of 

 the numerous small vents that were once active in this region. Its 

 single peak is 460 feet in height. As there did not seem much 



