The second type of physical disturbance was volcanic activity which took place on a tremendous scale, and which appears to have started as a direct accompaniment of the Rocky Mountain Revolution. This igneous activity took place not only in the Rocky Mountains but also westward to and in the Sierra-Cascade Range, as well as in the mountains of western British Columbia and Alaska. This activity continued well into the succeeding Cenozoic era, and it is more fully considered in the next chapter. The third type of crustal disturbance took place on a large scale when the Appalachian Mountains, which had been almost wholly planed away by erosion during Mesozoic time, were reelevated from 1,000 to 3,000 feet by an uplifting force not accompanied by folding. All or nearly all of New York and New England, as well as much of southeastern Canada, were similarly upraised at the same time. This notable uplift of so much of eastern North America is a matter of great importance because the major relief features of that area have been produced by erosion or dissection of the upraised surface since late Mesozoic or early Cenozoic time. In view of the fact that this work of erosion took place almost wholly during the Cenozoic era, it will be discussed in the next chapter. In conclusion, brief mention may be made of the kind of climate of the Mesozoic era. As shown by the character and distribution of fossil plants and animals, the Mesozoic climate was in general mild and rather uniform over the earth, but with some distinction of climatic zones. Such distinction of climatic zones is unknown for the Paleozoic era, while it was notably less than at present. CHAPTER XVI MODERN EARTH HISTORY (_Cenozoic Era_) Since the Cenozoic era is the last one of geologic time, it will be of particular interest to trace out the main events which have led up to the present day conditions, especially in North America. Both because of the recency of the time and the unusual accessibility of the rocks, which are mostly at or near the surface, our knowledge of the Cenozoic era is exceptionally detailed and accurate. It will, therefore, be more necessary than ever to select only the very significant features of this history for our brief discussion. During the first half of the Tertiary period portions only of the Atlantic coastal plain were submerged under shallow water, but soon after the middle of the period (Miocene epoch) the sea spread over practically the whole Atlantic coastal plain area from Martha's Vineyard south to and including Florida. During the late Tertiary the marine waters had become greatly restricted, and by the close of the period the sea was entirely excluded from the Atlantic seaboard. The total thickness of these Tertiary strata is less than 1,000 feet, and they all tilt downward gently toward the sea. The strata consist mostly of unconsolidated sands, gravels, clays, marls, etc.