Truly excellent though popular in approach, Idyll's book, at once more thorough and less lyrical than Rachel Carson's monograph, is as much about the sea around us as about deep oceanic abysses. Man's awe and ignorance of the ocean floor and its creatures is stupendous. Its greatest depths occur in trenches near great island arcs, mainly in the Pacific. There is considerable life down on the bottom which the author displays in a lengthy sampling of species, protozoa, molluscs, fish and gelatinous masses. He outlines great mysteries still unsolved: how were the great crevices formed? will we ever know the facts behind the eel's fantastic migratory instinct to the Sargasso Sea? His explanation of bioluminescence (light made by fish in utter blackness) is particularly absorbing. The abyss also gives up a high incidence of archaic life forms that have retreated into it and adapted to the pressure and cold, preferring not to compete with creatures in shallower areas. Much to the author's joy, a movement is underway to drill a hole through the earth's crust, beginning in deep ocean where the crust is thinnest.... Out of these depths, much fascinating material is retrieved to reward readers of all ages.