5 14 THE TERTIARY PERIOD 



Yellowstone Park continued to be an active volcanic centre, and 

 was characterized by great ejections of basic andesites and basalts, 

 both lavas and tuffs. 



The close of the Miocene in North America was marked by 

 some extensive geographical changes. Central America and the 

 Isthmus were upheaved, joining North and South America, and 

 cutting off the connection between the Atlantic and Pacific. The 

 effects of this land bridge were soon made evident in the intermi- 

 grations of the land mammals which had been peculiar to one or 

 other continent, South American types appearing in North Amer- 

 ica and vice versa. The same movement elevated the West Indian 

 islands, and joined Florida to the mainland, adding at the same 

 time a narrow belt to the Atlantic and Gulf coasts. Along the 

 Pacific coast an upturning of the strata and elevation of the moun- 

 tain ranges took place, though subsequent movements added much 

 to the height of the mountains. 



Foreign. — In the north of Europe the sea retreated from large 

 areas ; northern Germany was now dry land, with only a relatively 

 small bay invading it, while England was entirely above water, and 

 has no marine Miocene beds. On the west coast of Europe, the 

 Atlantic encroached largely, as in France, Spain, Portugal, and also 

 the northwest of Africa. Spain was joined to Africa, but straits 

 across northern Spain and southern France connected the Atlantic 

 with the Mediterranean. Another change of great importance was 

 the shutting off of the long-standing connection of the Mediter- 

 ranean with the Indian seas. The former covered much of east- 

 ern Spain, and flooded the lower Rhone valley, sending an arm 

 along the northern border of the Alps to the neighbourhood of 

 Vienna. Here it expanded into a broad basin, connected with 

 another great basin covering Hungary. Most of Italy, Sicily, and 

 a large part of northern Asia Minor were under water, but the 

 Adriatic and ^Egean Seas were mostly land, and the Alps formed a 

 chain of islands, mountainous, but not nearly so high as at present. 



At the end of the Lower Miocene came a great upheaval of the 

 Alps, by which the sea was again excluded from that region, and, 

 just as in the Oligocene, inland seas and lakes took the place of 



