OLIGOCENE 507 



tant to follow the European scale, wherever that is practicable. 

 No marine beds are yet known in North America belonging to 

 this series, but in the interior region are extensive fresh-water 

 deposits which clearly should be referred to it, and which form 

 the White River stage. The largest body of water of this time 

 occupied northeastern Colorado, southeastern Wyoming, much of 

 western Nebraska, and South Dakota. A second lake of unknown 

 extent was in North Dakota, and may have been joined with the 

 first; the present severance of the deposits may be due to the 

 removal of the strata over the intervening territory. A third and 

 much smaller area is in the Cypress Hills of the Canadian North- 

 west Territory. The strata formed in these waters, partly fluvia- 

 tile and partly lacustrine deposits, are almost perfectly horizontal, 

 and consist of pale-coloured, moderately indurated sands and clays, 

 which weather into fantastic bad lands (see Figs. 23, 24, pp. 

 79, 80; Fig. 133, p. 317). In the South Park of Colorado, at 

 Florissant, was a very small lake, probably of Oligocene date, in 

 which showers of fine volcanic ashes formed thin, papery shales, 

 which have preserved great numbers of plants and insects. 



No very marked disturbance closed the White River age ; the 

 lakes were simply filled or drained and deposition ceased. 



Foreign. — During the Eocene nearly all Germany had been 

 land, but in the Oligocene it was invaded by the sea, which broke 

 in from the north and covered all the northern plain, extending 

 into Belgium, and sending long bays to the south. One of these 

 reached to the strait on the north of the Alps, expanding into 

 a large basin near Mayence and Frankfort. Over Germany the 

 sea was shallow, permitting the formation of extensive peat bogs, 

 where were accumulated ' masses of lignite or brown coal. In 

 the basin of Paris the sea had a greater extent than in Eocene 

 times, though with lacustrine beds intercalated, but in England the 

 beds are more of brackish- and fresh-water origin. In southern 

 Europe the sea retreated from wide areas, and in its place were 

 extensive bodies of fresh and brackish water, in many of which 

 peat bogs accumulated masses of lignite. Such lignitic deposits 

 occur at intervals from the south of France, Switzerland, and 



