210 GLACIAL HISTORY. 



home with the erratic blocks and masses of debris which have 

 been dispersed from the Valais over the Jura, it has probably 

 issued originally from the same region, and was transported at 

 the same time *. 



These phenomena lead Prof. Heer to believe that the date of 

 these colonies of Alpine plants belongs to the Glacial epoch. 

 At that time probably an Alpine flora was spread over the 

 plain, clothing the moraines and those spots that were not 

 covered by ice with the same flowers which now so charmingly 

 adorn the solitudes of the great Swiss glaciers. When after- 

 wards the glaciers retreated and the formation of the lignites 

 began, the flora of the plain advanced into this region, while the 

 Alpine flora took refuge in the mountains. When the country 

 was again covered with glaciers, the Alpine flora descended to 

 the plain, and a second time abandoned the low country as the 

 glaciers retreated to a higher region. Hence in the existing 

 vegetation the Alpine flora forms the most ancient element, 

 and it was probably dispersed at two different periods over the 

 whole country wherever the land was free from snow and ice. 

 With a change of climate the flora of the plain gradually ad- 

 vanced, and became so completely dominant that at last only a 



flora are found Campanula pusilla, Saxifraga aizoides, Linaria alpina, Gypso- 

 phila repenSj and Polygonum viviparum, which are met with everywhere in 

 the glacial soils and on the ancient Alpine moraines. Besides these species, 

 Prof. Heer also met with Saxifraga opposite/alia, S. muscoides, Ranunculus 

 alpestris, Asplenium septentrionale, Silene rupestris (at the Passwang), Heli- 

 anthemum alpestre, Primula auricula, Erigcron alpinus, and Aster alpinus, 

 which grow in the fissures of Alpine rocks. Hence these plants of Alpine 

 origin may have reached the Jura by the immense moraines and monstrous 

 blocks which no doubt formed real islands on the sea of ice. 



* The rusty-leaved Alpine rose (Rhododendron ferruaineum') also occurs on 

 a great block of St.-Gothard granite at the Axenstein, above Brunnen. It is 

 probable that it descended from the St. Gothard with the immense blocks of 

 granite which are dispersed over the whole terrace of Morschach. In the 

 Canton of Aargau erratic plants are also met with on ancient moraines; 

 thus Alnus viridis grows upon a thick bed of loess, which rests upon the 

 White Jura of Waltersburg. In the same way, near Schonenwerth, in the 

 valley of Jonen, Prof. Heer has seen Viola liflora upon an Alpine block j and 

 Asplenium septentrionale occurs upon a block of granite near Kiiuten. (See 

 Miihlberg, die erratischen Bildungen im Aargau, p. 184.) 



