GEOGRAPHICAL EVOLUTION 361 



Jungles and buried them under sand and mud, where they 

 were eventually compressed into coal. To this united 

 co-operation of dense vegetable growth, accumulation of 

 sediment, and slow subterranean movement, Europe owes 

 her coal-fields. 



All this time the chief area of high ground in Europe 

 appears still to have lain to the north and north-west. The 

 old gnarled gneiss of that region, though constantly worn 

 down and furnishing materials towards each new formation, 

 yet rose up as land. It no doubt received successive eleva- 

 tions during the periods of disturbance, which more or less 

 compensated for the constant loss from its surface. 



The next scene we may contemplate brings before us a 

 series of salt lakes, covering the centre of the continent 

 from the north of Ireland to the heart of Poland. These 

 basins were formed by the gradual cutting off of portions 

 of the sea which had spread over the region. Their waters 

 were red and bitter, and singularly unfavourable to life. 

 On the low intervening ridges a coniferous and cycadaceous 

 vegetation grew, sometimes in quantity sufficient to supply 

 materials for the formation of coal-seams. The largest of 

 these salt lakes stretched from the edge of the old plateau 

 of Central France along the base of the Alpine ridge to the 

 high grounds of Bohemia, and included the basin of the 

 Rhine from Bale down to the ridge beyond Mayence, which 

 has been subsequently cut through by the river into the 

 picturesque gorge between Bingen and the Siebengebirge. 

 This lake was filled up with red sand and mud, limestone, 

 and beds of rock salt. Where the eastern Alps now rise 

 the opener waters were the scene of a long-continued 

 growth of dolomite, out of which in later ages the famous 

 dolomite mountains of the Tyrol were carved. 



These salt lakes of the Triassic period seem to have 

 been everywhere quietly effaced by a widespread depres- 

 sion, which allowed the water of the main ocean once more 

 to overspread the greater part of Europe. This slow sub- 

 sidence went on so long as to admit of the accumulation of 

 masses of limestone, shale, and sandstone, several thousand 

 feet in thickness, and probably to bring most of the insular 

 tracts of Central Europe under water. To this period, 



