CLIMATE OF PLEISTOCENE PERIOD. 45 



land-plants are preserved ; they occur far less frequently in a 

 recognisable condition than the shells of molluscs and the hard 

 parts of mammals. The fossiliferous Pleistocene deposits, as 

 we shall learn in subsequent chapters, consist chiefly of river- 

 gravels and loams, and of accumulations formed in caves and 

 rock-fissures. But the river which carries along sand and gravel 

 will as a rule sweep the debris of land-plants out to sea. The 

 few plants which may now and then become embedded will 

 often be macerated, rubbed, and water- worn, those tender parts 

 upon which botanists chiefly rely for the determination of 

 species being as a rule destroyed. Again, loose deposits of 

 gravel and sand are not good preservers, for they allow water 

 to soak through them more or less freely, and thus any plants 

 they may contain will tend to decompose past recognition. 

 Thus it is only now and then that plant-remains are found in 

 the river-deposits of Pleistocene times, and these consist chiefly 

 of water-worn sticks and logs. In cave-accumulations it is by 

 the merest accident that plants coidd become preserved, and in 

 point of fact almost the only traces that occur in such deposits 

 consist of the more or less charred relics which mark the sites 

 of ancient Palaeolithic hearths. Occasionally, however, we come 

 upon beds of vegetable matter buried under lacustrine accumu- 

 lations, and from these much important evidence has been 

 gathered. And not less noteworthy are those masses of cal- 

 careous tufa or travertine which have been formed upon the 

 borders of incrustating springs and cascades, for they have fre- 

 quently preserved leaves, seeds, fruits, and other remains of 

 plants, together with quantities of shells. Among the most 

 interesting of those tufa deposits are those of Lipari and Tus- 

 cany, described by M. Ch. Th. Gaudin j 1 those of Castelnau and 

 other places, near Montpellier, examined by M. G. Planchon ; 2 

 those of Provence, made known to us through the admirable 



1 Mem. de la Soc. Helv. des Sci. Nat. t. xvii. ; Bull, de la Soc. Vaud. des 

 Set. Nat, t. vi. p. 459. 



2 Bull. Soc. Bot. France, t. iv. p. 582 ; Etude sur les Tufs de Montpellier, 

 1864. 



