Geology for the layman by a seasoned pro who understands that not everyone can follow John McPhee--and that earth science courses are often underrated as ""rocks for jocks."" Parker, founding editor of Contributions to Geology, and past professor at the U. of Wyoming, paints a broad canvas covering such fundamental topics as the formation and age of the earth, radiometric dating, and the early atmosphere, as well as more refined geological matters like the rarity of gold, why the sea is salt (with an aside on Lot's wife), and problems of comparative stratigraphy. In addition, there is much discussion of paleobiology and evolution, including a reasonable explanation for what appears to be a billion year period between the first photosynthetic algae and the accumulation of sufficient atmospheric oxygen to account for the passage from anaerobic to predominantly oxygen-dependent life forms. Parker concludes this short but wonderfully rich volume with his own theory of ""gradual catastrophism."" Clearly there are irreversible geological events that mark time's unidirectional arrow in earth history. But there is also evidence of repetition: cyclical layerings in sedimentary rock strata, for example. Parker believes these repetitions reflect cyclic releases of stored energy--derived ultimately from the sun or from the earth's radioactive center. ""Catastrophes are just cyclic events that result from large energy storage capacity. . . gradualism. . . applies only to the way energy is provided to the system."" No doubt geologists will argue the point. But readers needn't worry. All else is finely--and solidly--wrought. Very scrutable.