Page:Washington, A Guide to the Evergreen State.djvu/45

10 altered in structure and recrystallized. Paleozoic rocks found in various places across northern Washington contain valuable fossil specimens of marine life of that period.

During the Mesozoic era, which probably lasted for more than 100,000,000 years, the essential features marking the existing topography were formed. It was during the latter part of this era (Jurassic period), according to John Hodgdon Bradley, that the original uplift of the Sierra Nevada, the Coast Range, the Cascades, and the Klamath Mountains occurred. Also in this period, another great inundation laid down beds of mud and sand that gradually were transformed into the bedrock of the San Juan Islands. Large deposits of magnesite, especially in Stevens County, probably originated at this time. With the making of mountains, great masses of molten rock pressed upward through the earth's crust, and gold, silver and other metals were fused with the rock while in this liquid state. As the Cascades first, and later the Coast Range, were formed, successively they made new coastlines, low-lying barriers to the ocean. The Mesozoic era, the age of reptiles, gave to the world some of its most curious life forms, including the giant dinosaurs; many of these have been unearthed on the San Juan Islands and in other parts of the State. Many marine specimens have been found in the shales and limestones of Stevens County.

The latest era, the Cenozoic, was marked by some of the most dynamic changes of all, including the greatest lava flow in geologic history and the age of ice; it also gave to the region some of its most productive natural resources—rich soil left by extensive lava flows, the great rivers and bays taking shape during this period, and the rich deposits of coal and other minerals being laid down. Of this era, the last 2,000,000 years constitute the recent epoch, within which came great volcanic eruptions and the period of glaciation. The Tertiary period, enduring for more than 50,000,000 years, was marked by long periods of sedimentation, erosion, and vegetation, alternating with periods of immense volcanic activity.

The western part of the State, except for the highest, or central, part of the Olympic Mountains, was covered with water, and great swampy flats extended along the edge of the present Puget Sound Basin. From these were derived the shales and sandstones, the gull-bearing gravel of Sauk River, the commercial coal deposits. Gradually the sea floor was raised, and the Olympics were united with the mainland. Volcanic action, accompanying the building of the Columbian Plateau, brought forth great streams of lava, covering more than 200,000 square