TIIK PLIOCENE SEIJ1KS 601 



middle divi>im consists ul' clay, sand, and gravel in irregular layers, 

 and contains a mixture of marine ami freshwater shells with many 

 mammalian IKUU-S ; it received its name of " Forest Bed" from the 

 frequent occurrence of stumps, logs, and matted roots of trees, but 

 the-e are not in the position of growth, as formerly supposed ; they 

 lia\v all Kern drifted, though probably not from any great distance, 

 and Mr. Reid concludes that they grew on the side of a steep river- 

 bank which was continually being undermined and washed away 

 by thr current, "and settling generally in an upright position, as we 

 should expect from the greater density of the roots and from the 

 weight of the adhering soil, they have formed ' snags ' in the river, 

 such as are constantly met with in streams flowing through a forest- 

 clad country." 



The upper surface of this estuarine deposit is often weathered 

 into a soil and penetrated by small roots (hence termed the Eootlet 

 Bed), and is in some places covered by lacustrine deposits containing 

 freshwater shells, with remains of Fish, Amphibia, and small 

 Mammalia ; this is the Upper freshwater bed. 



The marine Mollusca, of which there are only nineteen species, 

 all occur in the Weybourn Crag, and include some extinct 

 species, as Melampus pyramidalis, Tellina obliqua, and Nucula 

 Cobboldia:. 



With respect to the land and freshwater Mollusca these number 

 sixty-two, of which thirty-three also occur in the Norwich, Chilles- 

 ford, and Weybourn Crags. Of the others, which do not occur in 

 older beds, some are extinct, e.g. Viviparus gibbus, Limax modioli- 

 formis, Nematura runtoniana, and Pisidium astartoides, and some no 

 longer live in Britain, e.g. Hydrobia marginata, H. Steini, Valvata 

 ' i Us, and Corbicula fluminali*. 



The mammalian remains are also numerous and important, and 

 when the species are arranged in three groups, as below, it is seen 

 that they prove the beds to have been formed just at the epoch of 

 transition from Pliocene to Pleistocene time, a certain number being 

 survivals from the Pliocene (either of Britain or France), and about 

 an equal number being new-comers which range to Pleistocene or 

 to modern times, while a few have not yet been found elsewhere. 



(1) Survivals from Pliocene, 19 



Elephas meridionalis. Cervus poligniacus. 

 antiquus. ,, Etueriarum. 



Rhinoceros etruscus. elaphus (stag). 



,, nicgarhinus. ,, verticornis ( = C. belgrandi). 



Hippopotamus major. Machierodus latidens. 



Equus stenonis. Trogontherixuu Cuvicri. 



,, caballus (horse). Castor fiber (beaver). 



