Estimates of geologic time have expanded rapidly and radically during, the present century. Many geologists have accepted the newer figures with hesitation, and some have expressed doubt that the geologic record justified them. As against the modern estimate of 60,000,000 years for Tertiary time, there still are geologic museums in which Mesozoic reptiles are dated only 6,000,000 years ago. This paper seeks to justify modern estimates from the geologic record itself. It makes no claim to new truth, but only to the presentation of new evidence and a new approach in support of certain modern conclusions.
Time estimates based on the geologic record must use present conditions of climate and land surface as a measuring rod except where there is direct evidence to the contrary. It is frankly recognized that the problem has too many unknown or little-known elements to yield exact data. This paper is . . .