In western North America, on the other hand, the strata of the Mesozoic-and of the cenozoic also-are widely spread.
"The Elements of Geology"
William Harmon Norton
The Paleozoic rocks are buried quite generally from view except where the mountain makings and continental uplifts of the Mesozoic and cenozoic have allowed profound erosion to bring them to light, as in deep canyons and about mountain axes.
"The Elements of Geology"
William Harmon Norton
It is therefore at the close of the Cretaceous that the line is drawn which marks the end of the Middle Age of geology and the beginning of the cenozoic era, the era of modern life,-the Age of Mammals.
"The Elements of Geology"
William Harmon Norton