1905] A Landslide on the Lievre River. i8q 



happens that the stiff and more coherent masses of clay are broken 

 down and mix with the softer material, the whole mass of clay, 

 sand and mud being tumultuously and irresistibly moved forward 

 and downward into the basin of the river. 



According to Mr. R. F. Stupart, Director of the Meteoro- 

 logical Office, Toronto, (see accompanying table,) the average 

 rainfall at Ottawa for the five months commencing June and 

 ending in October, for the past nineteen years, was 14.62 inches. 

 The rainfall during the summer of 1903 for a similar period was 

 19 44 inches. This abnormal precipitation doubtless contributed 

 in no small measure to the catastrophe. 



Sir William Logan, commenting on the cause of the Maskin- 

 ong6 landslip, was of the opinion that it was induced by "pressure 

 on an inclined plane assisted by water;" and though he was not 

 able to determine the nature of the subsoil, he believed, from a 

 survey of th? surrounding country, that it consists of Silurian 

 limestone, the dip of which is, where visible, in the direction of 

 the river. 



At no point, so far as our examinations extended, did the 

 Lievre landslide rench the underlying solid rock surface, the glid- 

 ing plane being in every case composed of the underlying imper- 

 vious clay or hard-pan. This very smooth and striated surface, 

 as shown in the accompanying illustration (Plate IV), was visible 

 at several points along the base of the hills, as also on the 

 western side of the wooded knolls situated near the river and 

 which were not affected by the movement. 



The motion must have been primarily determined by the 

 presence of rather contiguous and extensive sheets of the super- 

 saturated or semi-liquid clay; for it is obvious that no very steep 

 gradient existed throughout the entire distance. In fact, the ob- 

 servations made seemed to warrant the belief, that the gliding 

 plane was only steep in very close proximity to the rocky hills, 

 while a short distance away, it was more or less undulating with 

 only a gentle pitch outwards and downwards to the river. The 

 original level of the plain, at this point, averages about 25 feet 

 above the river, while the river itself is only about 20 feet in 

 depth. Much of the debris which eventually reached the river 

 was material once situated about 20 feet below the original 



