ANTIQUITY OJF MAN. 245 



beds of stalagmite in that cave would require even 

 half a million of years for their formation ; but obser- 

 vations in other caverns show that, under favourable 

 circumstances, beds of this thickness might be formed 

 in a thousand years. In point of fact, the solution of 

 limestone by carbon dioxide, and its deposition again, 

 is a process depending on the amount of organic 

 matter going to decay and furnishing acidulated water, 

 and on the exposure of this water to the air; and the 

 activity of this process must, in any particular case, 

 have varied very much in the lapse of time. The cal- 

 culation of Boucher de Perthes as to the growth of 

 the peat at Abbeville was supposed to give a period 

 of 20,000 years for its accumulation, and yet it all be- 

 longed to the time since the newer or Neocosmic age. 

 But his own observations show that it is a forest peat, 

 the growth of which must necessarily have ceased 

 since the original forest covering of the country was 

 removed; and the observations of D'Archiac show 

 that at present, in this same district, peat, where cir- 

 cumstances favour its growth, may accumulate at the 

 rate of more than two feet in a century. This Abbe- 

 ville peat was formed subsequently to the erosion of 

 the Somme valley, and the deposition of its " palaeo- 

 lithic " gravels ; and if the time required for the 

 growth of the peat has been exaggerated, so has that 

 for the older excavation and deposition. When one 

 considers the little river Somme flowing quietly in its 

 broad green valley, and asks how long time it would 

 require to cut this valley out of the chalk, and to 



