Page:Popular Science Monthly Volume 17.djvu/553

Rh irons (augite and hypersthene); 4. Feldspars in large crystals; 5. Microlithic granules of titaniferous oxide of iron; 6. Feldspathic microliths.

The general lava of the eruption of 1866 contains as inclosed masses lavas, the mineral composition of which differs considerably from that of the medium which surrounds them, of types which have a considerable part in the constitution of the ancient lavas of the volcano. The minerals of the recent lava are generally penetrated by foreign matters, microscopic inclusions which are sometimes crystalline, sometimes composed of amorphous matter. The latter inclusions are portions of the surrounding matter which remains inclosed in the crystals at the moment they are formed, and nearly always contain a bubble of gas, in which M. Fouqué found minute quantities of matter analogous in its properties to organic matter. Jets of ashes were cast out in many of the spurts of the eruption. These ashes are lava pulverized by the quick passage of gases and vapors through it while it was still more or less fluid. Its condition as to crystallinity depends on the condition of the lava at the moment it became an ash. The more fluid the lava, the more like pumice is the ash. If the lava has become charged with crystalline substances, especially if they are microliths, the ashes will offer the same characteristics. In the present case the ashes, being derived from lavas which were so crystalline that they were hardly fluid, were rich in crystals and microliths.

Remarkable movements of the soil have been produced by the eruptions within a limited space around the principal cones of the volcano, and have notably modified the surface of the land to that extent. These manifestations have always been special subjects of study with geologists.

Besides the phenomena already described, the complete development of an eruption involves: 1. The opening of the ground; 2. The formation of a cone or crater; 3. The production of a stream of lava. All these manifestations took place during-the last eruption at Santorin. Eruptions analogous to those of 1866 have taken place in the Bay of Santorin since the beginning of the historical period, and have given rise to the islands which are known as the Kamenis. The bay itself was created by a catastrophe which was anterior to history, for no writer of antiquity mentions it. Yet remains of habitations have been discovered in the lava, with numerous objects and domestic utensils, which lead to the conclusion that a civilized population, who had already developed artistic tastes, were its witnesses and victims. Judiciously conducted excavations and microscopic examinations of their potteries have furnished much information concerning these ancient people. They were laborers and fishermen; they had flocks of goats and sheep, cultivated grain, made meal, extracted the oil from olives, wove cloths, fished with nets, and lived in houses with walls of squared stone and wooden beams. Most of their tools were of stone, the