PLEISTOCENE OF EUROPE, NORTH AP^RICA, AND NORTH AMERICA 393 



favors the theorj" that tlie Forest Bed deposits were accumulated during 

 an epoch of genial conditions which succeeded a colder glacial period in 

 which the Chillesford and Weybourn Crags were deposited; these 'crags' 

 mark the culmination of the cold conditions which began to manifest them- 

 selves as early as the Red Crag (p. 317) of Upper Pliocene times; at this 

 culminating time the sea abounded in arctic molluscs. Even in the Red 

 Crag, northern forms of molluscs begin to appear, and when we reach the 

 Chillesford and Weybourn crags the marine molluscs present a decidedly 

 arctic aspect. Immediately above the Weybourn Crag there is evidence of 

 a climatic reaction, because the estuarine and fluviatile deposits of the 

 Forest Bed contain a flora and a mammalian fauna of temperate type 

 which contrast strongly with the assemblage of northern and arctic shells 

 in the subjacent crag dei30sits. 



Flora of the Norfolk I titer glacial. — All the plants composing the Norfolk 

 Interglacial flora belong to living species, and with a few exceptions are 

 still indigenous to Norfolk, including such forms as the maple, hawthorn, 

 elm, birch, alder, hornbeam, beech, pine, and spruce. The arrival of the 

 • spruce {Abies) is especially noteworthy because, although known in Miocene 

 times in the arctic region of Grinnell Land, this is its first appearance in 

 central Europe ; it is also found in the interglacial lignites of Switzerland. 

 It has since constituted an important member of the European forests. 

 From this tree flora Reid concludes ^ that the climate was nearly the same as 

 the climate of present times, but slightly warmer. This is in latitude 52° 40'.^ 



Contemporaneous with this temperate flora there flourished the remark- 

 ably rich mammalian fauna of the Forest Bed; the mammals also indicate 

 conditions of climate somewhat warmer than those prevailing in the south 

 of England to-day. 



Mammals of the Norfolk Interglacial Epoch 



For our knowledge of the mammalian life of the Forest Bed and contem- 

 poraneous fauna in France we are principally indebted to Dawkins (1880, 

 1883), to Newton (1880), to Gaudry (1893), to Boule (1902), and Pohlig 

 (1907). Dawkins many years ago (1883, p. 579) gave the ratio of living, 

 extinct, resident, and newly arriving mammals as follows : 



Survivals from the Pliocene 11 species 



Newcomers, extinct forms 6 " 



living " 21 " 



The specific determinations of many of these animals, especially of the 

 horses and the deer, await revision, and upon this closer study depend many 



' Reid, C, and Rcid, E. M., The Pre-Glacial Flora of Britain. Jour. Linn. Soc, Botany, 

 Vol. XXXVIII, .Jan., 1908, pp. 206-227. 



^ A list of these plants is given in Dawson's The Geological History of Plants, 1896, 

 pp. 218-271. 



