500 A. Blytt on the probable Cause of 



1875) with 4 alternations ; arc 13'. And with these the 

 marine formations of the Vienna-basin, Hungary, and Tran- 

 sylvania come to a close. Volcanic outbursts commenced in 

 these countries even in the Oligocene period ; they became 

 very frequent in the Miocene, and during this period the Alps 

 rose to great altitudes. 



In the basin of Mayence the marine Oligocene formations 

 (Weinheimer marine sand and Septaria-clay) are followed first 

 by a freshwater formation ; then the Miocene period com- 

 menced with a depression. But during volcanic eruptions the 

 basin was upheaved and became more and more freshwater. A 

 continuous formation of beds took place. Over the Cerithium- 

 limestone, the Corbicula-limestone and Littorinella-clay were 

 deposited, in all with 20 or more alternations (according 

 to Lepsius, Das Mainzerbecken) . All these deposits are 

 Miocene. 



We now pass further forward in time. The Pliocene has 

 four oscillations, 13', 14', 15', and 16'. We have already 

 mentioned the Congeria-beds of the Vienna-basin. In Eng- 

 land there are three oscillations : — Coralline Crag (14'), Eed 

 Crag (15'), and Cromer Clay or Westleton Shingle (16'). 

 Profiles of these are to be found in Quart. Jouru. Geol. Soc. 

 Lond. 1871 (by Prestwich). The climate of Europe began to 

 become colder in the Pliocene. Even the oldest deposit in 

 the Pliocene of England contains stones which niay have 

 been grooved by ice, and at the close of the Pliocene there 

 w^ere already great glaciers ; the Pliocene was followed by the 

 Glacial epoch. We have seen how, during strong and ex- 

 tensive volcanic action, previously marine basins were during 

 Oligocene, and especially Miocene, times uplifted above the 

 sea not to be depressed afterwards (Paris, Vienna, Hungary, 

 the Mayence-basin, and we may add Switzerland), and we 

 have seen that the Alps were upheaved in Miocene times. The 

 Faroes and Iceland were built up, at any rate in great part, 

 at the same time by basalts and lavas ; perhaps, moreover, 

 the submarine bank which connects Europe with Greenland 

 was uplifted during the last portion of the Miocene period. 

 In the Mediterranean, according to Neumayr (see Suess, 

 Antlitz der Erde, i. p. 425) the coast-lines at the close of the 

 Pliocene lay even lower than at the present day. No doubt 

 all these elevations have had much influence upon climate. 

 Changes in the length of the day are dependent upon varia- 

 tions of the eccentricity. Geographical changes follow upon 

 the increase of the day, and climate changes with the distri- 

 bution of land and sea. 



The Coralline Crag in England (according to Prestwich) 



