{submerged} 85-585 ⅝-4⅝
CENOZOIC 0-80 0-½
MESOZOIC 80-180 ½-⅞
PALEOZOIC 180-570 ⅞-4⅞
PRECAMBRIAN 570- 4⅞-
As the end of the Cretaceous Period approached, slightly more than 80
million years ago, the flat monotonous landscape (fig. 41) which had
prevailed during most of Late Cretaceous time gave little hint that the
stage was set for one of the most exciting and important chapters in the
geologic history of North America.