282 LECTURE X. 



This portion of the alluvium is^ on account of its colour, fre- 

 quently called grey diluvium. 



" 3. Deposition of calcareous loam, called loess, whicli always 

 contains lime knolls of the same shape, whether on the banks 

 of the Rhine or at Paris, which overhes the preceding stratum, 

 and marks a new phasis in the quaternary period. 



" 4. Formation of a gravelly deposit, the broken flints of which 

 are cemented in red loam and quartzose sand, which contains no 

 organic remains, is never clearly stratified, and lies partly upon 

 the grey diluvium, partly upon the loess, as may be plainly 

 seen in the vicinity of the new church of the Quartier de Deux 

 Moulins, or upon the calcaire grassier, as may be seen on the 

 platform of Maison Blanche and Montrouge. 



" This deposit, usually called the red diluvium, which was 

 previously, but erroneously, believed to be overlaid by the 

 loess, lies mostly in channels, which are scooped out in the sub- 

 jacent strata. All geologists know the singular bag-like de- 

 pressions, which sometimes form well-shafts of five, ten, and 

 fifteen meters in depth, intersecting both solid and moveable 

 stone masses. These also are the effects of different pheno- 

 mena of the quaternary period. 



''When the subjacent diluvial strata, where they are in contact 

 with the deposit, show no excavation, there are seen in the 

 bottom one or two horizontal layers of firm brown or reddish 

 clay, which sometimes contains a layer of ferruginous sand ; 

 and if bag-shaped depressions are present, this clay lines their 

 walls, and thus envelopes the red diluvium, which it separates 

 at the same time from the loess and the grey diluvium. 



" The red diluvium spreads generally over the ground and 

 the side walls of our partly filled up valleys ; and rises in the 

 vicinity of Paris to a height of at least sixty-five meters, but 

 does not reach the heights attained by the loess. 



" 5. The surface of the red diluvium was itself washed off by 

 the waters, which stratified its upper masses, and mixed it 

 with grey loam. This deposit is still seen at the gate of Ivry. 



" 6. After these successive processes our valleys were again 

 scooped out, but manifestly under new conditions. The de- 

 posits hitherto mentioned adhered to the walls of the valleys. 



