84 NEW YORK STATE MUSEUM 



on account of its ready absorption of water and its high degree of 

 mobility when thoroughly soaked. They are perhaps the best 

 illustrations of flow on small gradients that have yet come to notice. 

 The flow of May 7, 1888, on the Riviere Blanche, near the village 

 of St Casimir, Quebec, is described by Chalmers^ as having had a 

 length of 1050 yards and an extreme width of 600 yards, yet the 

 descent of the bed for the whole distance was only 27 feet or only 

 10 inches in 100 feet. The volume of the disturbed clay was esti- 

 mated by G. M. Dawson^ at 93,654,000 cubic feet. An occurrence 

 at St Alban in the same vicinity, on April 27, 1894, is described by 

 Monsigneur Laflamme,^ who placed the volume of the flow at from 

 600 to 700 millions of cubic feet. In the disturbance that took place 

 on the Lievre river, October 11, 1903, according to Ells,* the satu- 

 rated mobile clay was not the surface layer but a bed lying some 20 

 feet deep into which the water penetrated from below, and the 

 surface materials floated on this moving mass which found an out- 

 let on the extension of its bed. The occurrence had thus points of 

 similarity with the slides described under class 4. Other extensive 

 slides in this region are on record or evidenced by present con- 

 ditions, the first published description of them having been given 

 by Sir William Logan. ^ 



In flows of very fluid materials like the Leda clay it is not neces- 

 sary that the bed or slipping surface have any pronounced slope, so 

 long as there is a favoring surface contour. The initial stress may 

 come from a preponderance of weight on one part of a buried 

 horizontal layer compared with the weight exerted at another 

 point, the stress thus set up causing a general movement of the 

 whole mass toward the unweighted ground. If the surface layer is 

 coherent and does not follow the motion of the lower bed but sub- 

 sides in place, the slide takes on the character described under class 

 4 or 5.. 



3 Earth slides. These refer to disturbances of earthy materials 

 in a nonfluid state, such as take place on a relatively high slope and 

 resemble earth avalanches in mountain regions. They arise in 



1 Report on the Geology of the Three Rivers Map Sheet. Geol. Surv. 

 Can. Ann. Rep't. v. 11, p. 62 J. 1900. 



2 Remarkable Landslip in Portneuf County, Quebec. Geol. Soc. Ann. 

 Bui. 10, p. 487. i899-i'900. 



3 Trans. Roy. Soc. Can., v. 12, pt 4, p. 631 1894. 



4 The Recent Landslide on the Lievre River, P. Q., Geol. Surv. Can. Ann. 

 Rep't, v. 15, p. 136 A. 1906. 



5 Proceed. Geol. Soc. London, v. 3, p. 767. 



