Country Basalts at www.japanese-home-gardens.com

Kushiro's experiments tie in well with the observed distribution of lava types in many parts of the world. It had been shown in the islands of Japan, for example, that the composition of lavas poured out by volcanoes varies with geographical location. In a long belt down the east side of the country basalts the basalts are of the silicon-rich variety. Those on the west side of the country basalts are poorer in silicon and richer in alkalies. This correlates well with the distribution of earthquakes in Japan. Those in the east part of the country basalts originate at shallow levels whereas those to the west are deeper. If the process of melting and earthquake production are related in some way, as it seems reasonable to suggest, these different lava types in Japan must originate at progressively deeper levels as one goes westward.

The partial melting of the rocks beneath the earth's crust produces basalts (finegrained extrusive lavas), dolerite (medium-grained intrusive rock) and gabbro (coarsegrained intrusive rock) [7]. Basalts form the floors to the oceans and occur extensively in Iceland and in some continental areas. Dolerites are found in thin extensive sheets called dikes and sills [5] injected in or between the sedimentary rock layers. Gabbro occurs in large layered intrusions which were the source of the dolerite and basalt.

During the past year there have also been noteworthy developments in the study of the problems associated with the origin of two of the commonest rocks in the earth's crust— basalts and granites. All of these topics are controversial and subject to heated debate. This is characteristic of rapidly developing fields of study in which conjecture tends to outstrip observation and experiment.