Ninety-nine and nine-tenths of the earth’s volume must forever remain invisible and untouchable. Because more than 97 per cent of it is too hot to crystallize, its body is extremely weak. The crust, being so thin, must bend, if, over wide areas, it becomes loaded with glacial ice, ocean water or deposits of sand and mud. It must bend in the opposite sense if widely extended loads of such material be removed. This accounts for … the origin of chains of high mountains … and the rise of lava to the earth’s surface.

At bottom each “exact” science is, and must be speculative, and its chief tool of research, too rarely used with both courage and judgement, is the regulated imagination.

Ninety-nine and nine-tenths of the earth’s volume must forever remain invisible and untouchable. Because more than 97 per cent of it is too hot to crystallize, its body is extremely weak. The crust, being so thin, must bend, if, over wide areas, it becomes loaded with glacial ice, ocean water or deposits of sand and mud. It must bend in the opposite sense if widely extended loads of such material be removed. This accounts for … the origin of chains of high mountains … and the rise of lava to the earth’s surface.

Earthquakes traveling through the interior of the globe are like so many messengers sent out to explore a new land. The messages are constantly coming and seismologists are fast learning to read them.