Fossil air bubbles in wet sand were shaken and consolidated by an earthquake, compressed to sandstone and eroded to the present state. Taken in the lower canyon of the Grand Canyon, where the canyon gives way to the impounded water of Lake Mead. As the Colorado River descends from an elevation of about 3100 feet at Lee's Ferry, some 280 miles to Lake Mead (1200 feet); it is also a journey back in time, cutting through some 1.7 billion years of geologic and paleontologic history. Every few mile