i88 The Ottawa Naturalist. [January 



Riviere Blanche landslip, they contained, when saturated, from 

 22 to 25 per cent, ot their own weight of water. 



2. Increased or unusual precipitation, which furnishes the 

 great excess of water necessary to produce that condition of 

 supersaturation of certain portions of the clay which eventually 

 brings about unstable equilibrium of the beds. Thus, certain 

 layers or portions of the clay are in a semi-liquid condition, and 

 examination ot the Lievre occurrence shows a considerable portion 

 of the clay to have about the same consistency as ordinary thin 

 porridge. The extra weight of the overlying material, due to the 

 unusually large amount of contained water, results in the displace- 

 ment of .those portions or blocks of land which are underlaid by 

 the supersaturated or liquid clay. Movement once begun gathers 

 force and quickly extends the area affected, and the existence of 

 even a very gentle gradient imparts an irresistible movement 

 towards the lower ground in the vicinity of the river. 



The flats which border the Liivre river in the neighborhood 

 of the recent landslip are principally made up of very thicK and 

 uniform beds of a stiff, impervious bluish-gray clay, with small 

 and subordinate layers of silty, sandy or gravelly material. This 

 drift material forms a plain, which, with very occasional minor 

 depressions, occupied by small marshes or creeks, extends to the 

 base of the rocky hills. Between this clay and the solid rock 

 beneath, along the base of the hills, there generally intervenes a 

 considerable layer composed of boulders or coarse gravel. Most 

 of the surface drainage from the rocky hills flows out along the 

 top of this plain, reaching the river through one or two small 

 brooks. A large proportion, however, of this surface water flows 

 downward through the coarse gravel and boulders, finding its 

 way into the various sandy or silty layers and thus feeding the 

 wells which are located on one or other of these layers. The in- 

 troduction of this water serves to produce the necessary degree of 

 saturation. During extreme wet seasons, like the summer of 

 1903, the amount of water thus flowing into and along these per- 

 meable layers must be very large, and with long continued and 

 unusual precipitation the saturated clay is being constantly in- 

 creased, until the limit is reached and the necessary conditions of 

 unstable equilibrium are produced. As a result it occasionally 



