Fourth division: The Mesozoic strata represent erosion and deposition as floodwaters retreated.
Third division: The Paleozoic strata comprising the Canyon's characteristic, horizontal strata formed in the early part of the flood.
However, the sections on geology and radiometric dating, written by Austin himself, are at a much more advanced, technical level.
On the other hand, the chapter dealing with the atmosphere is very elementary.
The numerous modern scientific arguments against Noah's flood have recently been discussed by Isaak (1998) and Wise (1998) among many others.
The oldest rocks are an Early Proterozoic (1700 Ma) crystalline basement (Vishnu Schists, intruded by Zoroaster Granites).
To evaluate and rebut the numerous specific creationist claims Austin presents, would require a book many times longer than second laws of thermodynamics (Wise 1998).
Austin (19) indicates that on Day 3 of creation week, molten Zoroaster Granite was intruded into Vishnu Schist.
Above these are Middle- to Late Proterozoic sedimentary and volcanic rocks, known as the Grand Canyon Supergroup, which were tilted and eroded before the deposition of the overlying Tapeats Sandstone of Cambrian age ( resembles a well-illustrated, geological textbook, replete with maps, technical diagrams, and references to scientific literature.
However its aim is to demonstrate unequivocally that the geology of the Grand Canyon is the product of creation week and Noah's flood, as determined by specific "literal" interpretations of the Book of Genesis.