THE PLIOCENE PERIOD. 



319 



In Belgium the thickness of the system is much greater, and con- 

 sists chiefly of sand. In France the system contains volcanic mate- 

 rial mingled with the sedimentary. The marine beds of southeastern 

 France (Rhone basin) are unconformable on older rocks, and reach 

 an elevation of 1150 feet. They extend up the valley of the Rhone, 

 and their limit in this direction marks the northern limit of the depo- 



Fig. 465. — Sketch-map of Europe during the Pliocene period. The broken lines 

 indicate areas of lacustrine and non-marine deposition. The full lines, the area of 

 marine deposition. (After De Lapparent.) 



sition in the southern Pliocene sea. The materials are largely uncon- 

 solidated. 



Among the alluvial and lacustrine beds of the period, those of 

 the basin of Mayence should be mentioned. They contain, along 

 with the ordinary varieties of sediment, lignite, with plants of North 

 American types. In the Vienna basin also are Pliocene deposits, 

 brackish water beds below and fluvial beds above. In Italy only, do 

 the Pliocene beds attain massive development. Along the Apennines, 

 the system has been variously estimated at from 1600 to 3000 feet 



