THE TERTIARY PERIOD 305 



of lava in the Sierras and Cascades. At that time the Miocene 

 gold-bearing stream gravels of California were buried under the 

 lava. Many well-known volcanic mountains, such as Shasta, 

 Hood, Rainier, etc., date from that time. In fact this period of 

 vulcanism has not altogether ceased at the present day, as shown 

 by a renewal of activity of Lassen Peak (altitude 10,437 feet) in 

 northern California on May 30, 1914. At the present writing 

 (October, 1915) there have been about 150 eruptions of the moun- 

 tain, in all cases fragmental materials only having been ejected 

 sometimes to a height of 5000 to 10,000 feet above the mountain 

 (Fig. 186). The eruptions of cinders and lava at Cinder Cone, 

 only 10 miles from Lassen Peak, occurred not over 200 years ago. 

 Other quite recent cinder cones are known in southern California 

 and Arizona. 



Foreign Tertiary 



Eocene. — Just after the emergence of much of Europe at the 

 close of the Mesozoic, there were certain basins of deposition such 

 as lakes, estuaries, etc. Early in the Eocene, however, a great 

 submergence set in, allowing marine waters to spread over a con- 

 siderable part of western and much of southern Europe. The 

 southeastern British Isles, the northern border of France, Belgium, 

 Holland, the northern border of Germany, the site of the Pyrenees, 

 Italy, all but the axis of the Alps, much of southeastern Europe, 

 and northern Africa were submerged (see Fig. 187). This greatly 

 expanded mediterranean of Europe also extended eastward across 

 southwestern Asia, except southern Arabia and southern India, 

 to connect with the Indian Ocean through the Bay of Bengal. 

 A narrow sound along the eastern side of the Urals connected 

 this mediterranean with the Arctic. In this vastly expanded in- 

 terior sea true marine deposition took place, the most character- 

 istic formation being known as Nummulitic limestone, so called 

 because it is chiefly made up of shells of a certain species (Num- 

 mulites) of unusually large Foraminifers. Perhaps no other 

 single formation in the crust of the earth built up essentially of 

 the remains of but one species of organism is so widespread and 

 thick, its thickness at times reaching several thousand feet. This 

 marine Nummulitic limestone now occurs at altitudes of 10,000 

 feet in the Alps, and fully 20,000 feet in Thibet. Limestone of 

 this age was quarried for the building of the Egyptian pyramids. 



