OSBORN, REVIEW OF THE PLEISTOCENE 255 



First Interglacial Stage — Norfolkian, Aftonian, Gunz-Mindel 



Immediately after the deposition of the Weybourn Crag in Essex there 

 is evidence of a climatic reaction because the overlying deposits, both 

 estuarine and fluviatile, of the so-called Forest Bed of Cromer (Norfolk) 

 contain a flora and mamimalian fauna of warm temperate type which 

 contrast strongly with the assemblage of the northern and Arctic mol- 

 luscs in the subjacent deposits of the Eed, Chillesford and Weybourn 

 Crags. From this classic locality of Norfolk the First Interglacial Stage 

 ■ has derived its designation Norfolkian. It is also known as the Cro- 

 mermn. 



The first cold period or glacial advance was succeeded both in Europe 

 and America by climatic conditions milder than the present. In the 

 Alpine region Penck and Bruckner have found evidences of a long 

 Gunz-Mindel interval of time, estimated relatively at 100,000 years, 

 which separates the climax of the first or Giinz glaciation from the sec- 

 ond or Mindel, but they believe that this First Interglacial Stage was 

 much shorter than the Second Interglacial. Owing to the warmth of 

 the climate the snow line of the Alps is believed to have risen 300m. 

 higher than at the present time. The deposits of this stage include the 

 PaludinenbanTc of northern Germany; these fresh-water deposits near 

 Berlin are of true interglacial time, since they lie between the deposits of 

 two Glacial advances. The most abundant species, Paludina alluviana, 

 has its present habitat far to the south on the borders of the Black Sea. 

 In general the other fresh-water and land molluscs belong to modern 

 species common to the same region to-day, indicating that climatic condi- 

 tions were not greatly dissimilar from the present. The plant remains 

 include the mosses and conifers, also indicating a climate similar to the 

 present, but they probably do not afford evidence of the higher ranges 

 of temperature which may have occurred at other times and places during 

 this First Interglacial Period. In America the deposits of this First 

 Interglacial Stage, known as the A f 'Ionian, are widely distributed and 

 yield a rich mammalian as well as a land molluscan fauna and abundant 

 plant remains which generally indicate a temperate to warm climate. 



HUMID FOREST CONDITIONS 



A striking characteristic of this interglacial stage is the evidence of 

 prolonged humid conditions of climate and abundant forestation favor- 

 able to forest-living mammals. There is no evidence either in the north 

 of Germany or in the northern United States of loess deposits such as 

 occur during the Second and Third Interglacial Stages and are believed 

 to be due to recurrent arid conditions and dust storms. 



