202 GLACIAL HISTORY. 



the deposition of the stratified mass which shows by its great 

 thickness that the glacier had disappeared from this spot for a 

 long time. In Eastern Switzerland, until recently, the upper 

 erratic formation only was known, which overlies the stratified 

 pebble-beds. At Utznach, in a section on the road to Gauen, 

 now again covered up, Prof. A. Escher de la Linth saw quite 

 distinctly the direct superposition of the lignite formation upon 

 the Miocene ; so that, at least at this point, there was no trace 

 of erratic blocks to be seen between the Miocene and the lig- 

 nites (see fig. 329, p. 152). At Durnten, also, the clays under 

 the lignite deposit only contain such stones as may have been 

 derived from the conglomerate of the surrounding hills. The 

 hypothesis of two glacial periods does not, therefore, seem to be 

 supported by the facts observed in Eastern Switzerland. Never- 

 theless, at Wetzikon, Alpine rocks showing all the signs of gla- 

 cial transport (see p. 151) are found under the lignites. This 

 deposit of lignite, however, is only of small extent ; but it lies 

 horizontally, and presents the same sequence of clay and coal 

 as at Durnten ; so that it cannot be supposed that these erratics 

 have got under the lignite deposit by displacement of the soil. 

 In Morschweil also, according to the investigations of Prof. 

 Deicke (p. 154), erratics are overlain by the lignites. 



Fortified by these facts, the conclusion may be adopted that 

 at two different periods glaciers invaded Switzerland, and that 

 the lignite formation occurred in the interval between them, 

 thus representing an episode of several thousand years in the 

 long Glacial epoch, the intercalated period having been sufficiently 

 long to diffuse over the low country a new vegetable covering. 

 The stratified deposits of rolled pebbles must have taken place 

 at the following periods : 1 . After the epoch of the lignites, 

 which may be called interglacial. 2. During the great exten- 

 sion of the glaciers, glacial drift. 3. After the second glacial 

 epoch, postglacial drift. 



For the Quaternary period the chronological order shown in 

 the following Table may be regarded as established : 



