In Part I, an attempt is made to determine the coefficient of viscosity of flowing lava. H. JEFFREYS already studied the flow of viscous liquid in an inclined channel of infinite breadth. Hitherto the formula deduced by him has been applied to the approximate determination of the coefficients of viscosity of flowing lava extruded in volcanic eruptions. Here, to make a more precise discussion, the flow of viscous liquid in an inclined channel of triangular section is studied: a formula to determine the coefficient of viscosity of the above flow is obtained by the method of dimensional analysis and the experimental coefficients contained in the formula are determined for various apex-angles of sections by the experiments with the flow of glycerine. As an example, the formula is applied to the lava flow extruded in the 1951 eruption of Mihara. In Part II, upwelling of lave from a central crater vent or a linear fissure is discussed as a Hagen-Poiseuille's flow. If the rate of lava flow, the height of lava accumulation corresponding to the residual pressure head at magma reservoir, the coefficient of viscosity of lava and the radius of the vent are known, the length of the vent from the crater to the reservoir can be estimated. This principle is applied to a few central eruptions, i.e. the dome formation on the summit of Tarumai in 1909, the overflow of lava from the Mihara crater in 1950 and the formation of lava fountain in the Sakurazima crater in 1958. The results obtained by these discussions are plausible and suggestive.

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Elastic wave velocity and thermal expansion of four kinds of volcanic rocks at high temperatures were measured. An increasing elastic wave velocity with a rise in temperature was observed in dacite from Showa-shinzan volcano and also in basalt from Mihara volcano, while a decreasing wave velocity was observed in andesite from Aso volcano. The stepwise increase in wave velocity of thermally treated Showa-shinzan dacite was observed at a certain temperature between 200℃ and 3000℃, while this stepwise velocity inclease was not observed in a virgin specimen in the first heating run. The wave velocity of Hakone dacite decreased with a rise in temperature from room temperature to 150℃ and then it increased at higher temperatures and again decreased stepwise at temperatures above 573℃. Thermal expansion of rock specimens was measured by a dilatometer. The remarkable difference of thermal expansion curves was related to the crystalline forms of free silica in rocks, namely quartz or cristobalite. The temperature variation of porosity was obtained from the difference between the measured and the calculated thermal expansion curves. An increase in wave velocity is generally correlated to the decrease in porosity. The inversion of a alpha to beta cristobalite is related to the stepwise increase in wave velocity in Showa-shinzan dacite.

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Muzina-goro is a neck-like mass of andesite, about 200m across and 70m high, intruded into the mudstone of the Ogawa formation of upper Miocene, in the western part of Nagano City. Vertical columnar joints are beautifully displayed. It is a composite mass composed of the andesite of tholeiite series (Vc type) in the interior, and of andesite of calc-alkali rock series (Vd type) in the margin (Fig. 1), and the two types gradually change to each other without a sharp boundary. By systematic sampling, it was possible to trace the course of crystallization and consequently to illustrate the genesis of the two types. Presence of phenocrystic pigeonite around augite is remarkable in the andesite of both Vc and Vd types. Although the two types are similar, small but distinct difference is observed between the two in their chemical composition as well as mineral composition. This difference can not entirely be attributed to the differentiation in situ, for the chilled margin is also composed of a similar andesite of Vd type. When the chemical composition of these various facies are plotted in the MgO-FeO+Fe₂O₃-Na₂O+K₂O diagram, they all lie within the area of calc-alkali rock series of this district. The ratio of rhombic pyroxene: total pyroxene (Rh + 100/Rh + Mo) in the groundmass varies in wide range, although these rocks are chemically much alike in the present case. Probably, the original magma was differentiated at the depth into two parts, which later successively intruded (Fig. 4). It may be postulated that high oxygen partial pressure, p₀₂, (Osborn, 1959) due to the contamination of water from the surrounding mudstone favoured the formation of calc-alkali rock series in the upper layer of the two parts separated at the depth. p₀₂ might also be higher in the margin than in the inner part when intruded in the mudstone. The wide variation of the ratio, Rh × 100/Rh + Mo, in the groundmass of calc-alkali rock series may be explained by the variation of p₀₂ in the chilled margin of these rocks. In this connection, it is noted that Fe₂O₃ content is higher in the contact part (M 2) than in the inner part (M 3), total iron oxide remaining the same.

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The Kami-goto district is located at the northern end of the Gotd islands, Nagasaki Prefecture, Southwest Japan, and occupies southwestern margin of the so-called Circum-Japan Sea alkali rock province. The district is devided in two; northern Uku district and southern Ojika district. In Uku district, andesites are mainly distributed, while basalts mainly develop in Ojika district. Generally speaking, the former belong to earlier eruption than the latter, both activities being in Quaternary age. Reaction phenomena between olivine and clinopyroxene have been observed in some but not all of the volcanic rocks which belong to the early stage fractionation, while it can be detected in all of the rocks of the middle stage fractionation. At the same time, large amounts of magnetite crystallize in the latter rocks. The volcanic rocks in Uku district show lower solidification index than 21, while those in Ojika district show higher index, and their chemical characteristics and fractionation trends are shown in Figs. 3 and 6. It can be seen in these figures that these rocks are plotted in a series which has similar tendency as the pigeonitic rock series of KUNO's classification but is situated nearer to Na + K, and represents the fractionation trend of iron enrichment. This kind of trend has never been found in alkali rock series of Japan and surrounding areas. An Extrapolated parental magma is shown in Table 5. This magma has subalkalic characteristic and contains higher amount of Na than K, and is considered to have oceanic characteristic rather than continental. From these results, it is considered that the volcanic rocks in the Kami-goto district were formed by fractional crystallization of subalkalic basalt magma. It is proposed to call these volcanic rocks "Kami-goto rock series".

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