POSTGLACIAL, &>c, DEPOSITS OF CONTINENT. 495 



grounds of France altogether, while some, such as LTypnum 

 scorpioides, still linger on. 



Peat-bogs, as I have said, attain their greatest development 

 in Northern Europe, but they are met with also not only in 

 Northern France, the Vosges, the Black Forest, Bavaria, and 

 Switzerland, but likewise in the mountains of Auvergne and the 

 Cevennes, in the Pyrenees, Northern Italy, and many other 

 elevated regions in the more southern parts of the Continent. 

 The vegetation of which they are composed has certain elements 

 in common, many of the plants being characteristic of Scandi- 

 navia and the north. Professor Ch. Martins has discussed the 

 origin of that peat-flora in a very interesting manner, and has 

 shown conclusively that it owes its wide dissemination to the 

 cold of the Glacial Period, 1 and Professor Heer has illustrated 

 the subject abundantly in his account of the present distribution 

 of the arctic-alpine plants of Switzerland. 2 The peat-bogs are, 

 as it were, asylums to which the northern plants, once common 

 to the low grounds of Europe, retreated in postglacial times, 

 driven out by the returning hosts of the temperate flora. And 

 they now flourish only in places which by reason of their 

 altitude, and sometimes simply on account of their humidity 

 and other unfavourable conditions, are not sought after by tem- 

 perate species. More recently, Professor Engler has reviewed 

 the whole question of the migrations of the various European 

 floras in a highly suggestive manner, and has shown that the 

 glacial or arctic element in the peat-flora is more marked than 

 might at first sight appear. Indeed he is of opinion that the 

 formation of the peat-bogs at the northern foot of the Alps began 

 during the Glacial Period. 3 



Of the other postglacial and recent deposits — the fluviatile 

 and lacustrine alluvia, shell-marl, calcareous tufa, etc., it is not 

 necessary to speak. They may be studied broadcast over the 

 Continent. It is enough to say that French, German, and 



1 Mem. de V Acad, des Sciences et Lettres de Montpellier, t. viii. p. 1. 



2 Die Urwelt der Schweiz, 2te Auflage, p. 582. 



3 Versuch einer Entwicklungsgeschichte der Pflanzenwelt, etc., I. Theil, p. 168. 



