Part 50

Glacial epoch, phenomena of, 287.

Glacier motion, cause of. 285.

Glossopteris and Gangamopteris flora, 136.

Gondwanaland, 136.

Gradient of temperature in Earth's surface crust, 126.

Haimanta period of India, 135.

Halley, Edmund, finding age by saltness of ocean, 13.

Hallwachs, photo-electric activity and absorption, 207.

Haloes, pleochroic, finding age of rocks by, 21; due to uranium and thorium families, 227; radii of, 227; over-exposed and underexposed, 228; intimate structure of, 229 et seq.; artificial, 229; tubular, in mica, 230; extreme age of, 231; effect of nucleus on structure of, 232; inference from spherical form of, in crystals, 233; structure of, unaffected by cleavage, 235; origin of the name "pleochroic,"235; colouration due to iron, 235; colouration not due to helium, 236; age Of, 236; slow formation of, 237, 238; number of rays required to build, 237; and age of the Earth, 238-241.

Hayden, H.H., geology of the Himalaya, 134, 138, 139.

Heat-tendency of the universe, 62.

Heat emission from the Earth's surface, 126; from average igneous rock due to radioactivity, 126.

Helium and the alpha ray, 214, 222; colouration of halo not due to, 236.

Hering, E., and physiological or unconscious memory, 111.

Herschel and Babbage theory of mountain building, 123.

Herschel, Sir W., on galaxy of milky way, 293.

Hertz, negative electrification discharged by light, 204.

Himalaya, geological history of, 134-139.

Hobbs, on association of earthquakes and geosynclines, 143.

Holmes, A., original lead in minerals, 20; age of Devonian, 21.

Horst concerned in Alpine deferlement, objections to, 156.

Hyperion, dimensions of, 177.

Ice, melting of, by pressure, 267 et seq.; expansion of water in becoming, 267; lowering of melting-point by pressure, 267; fall of temperature under pressure, 268 et seq.; viscosity of, 284.

Igneous rocks, average composition of, 43.

Inanimate actions, dynamic conditions of, 61.

Inanimate systems, secondary effects in, 63-65; transfer of energy into, 66.

Indian geology, equivalent nomenclature of, 139.

Initial recombination of ions due to alpha rays, 221, 222, 231; and structure of the halo, 231.