364 LECTURE SII. 



tionable as tliat of the stone-period, the bones of which are 

 certainly of a more recent date. 



Grillieronj who' discovered in the vicinity of the Zihl-bridge, 

 near Neufchatel, a pile-work of the stone-period, arrived at 

 similar results. The " culture bed^' has a thickness of at least 

 five feet, and lies below a layer of black mud, above which is a 

 bed of loam about five and a half feet thick, in which many 

 freshwater snails are found. The pile-work, which is visible 

 in the Zihl when the water is very low, was in the vicinity of 

 the spot where the former connection between the Neufchatel 

 and Biel Lake is narrowest, and amounts to at most 400 

 metres. The lakes, according to Gillieron, retreated slowly, 

 and the intervening space through which now the Zihl flows 

 was gradually filled up by moss and peat. 



This retreat, no doubt, took place very slowly, as the fine 

 alluvial mud is everywhere regularly levelled and stratified. If 

 now we were enabled to find an historical standard of this re- 

 treat, it might be applied to the whole distance from the pile 

 work to the Biel Lake, a distance of 12,800 Swiss feet, which 

 Gillieron only estimates at three kilometres. But in the vicinity 

 of the Biel Lake (Lake of Bienne) was built the old Abbey of 

 St. John between 1090 and 1106, so we may assume the date 

 1100. A document, prepared a century later, grants to the 

 convent the right of fishery from the poplars growing on the 

 shore of the lake, but which poplars no longer exist. At 

 present the convent is 375 metres distant from the shore. 

 Gillieron now assumes that the Abbey was built near the water, 

 and that this distance affords a measure for the alluvia accu- 

 mulated within 750 years. For greater certainty, he does not 

 measure the distance from the convent to the pile-work, but 

 to the point from which the lake regularly retreated, and, 

 assuming the distance to be 3,000 metres, he calculates 

 that 6,000 years at least were required for the retreat of 

 the lake. 



I say at least 6,000 years, for the assumption that the con- 

 vent was built on the margin of the lake is incorrect, but that 

 the convent people built at some distance from the lake, and 

 that the poplars, though nearer the water, were also planted 



