LANDSLIP IN PORTNEUP COUNTY, QUEBEC 489 



the absorption of the water and resulting, early in May, when tlie clay beds had 

 thus become thoroughly saturated, in the landslip which has been described. 



Protection from simii-ar Disasters 



The only way in which the recurrence of su9h slips in regions of country of the 

 same character and under similar exceptional conditions of precipitation can be 

 guarded against appears to be the provision of effective surface drainage, such as 

 to carry off the excess of water before the rather slow process of absorption by the 

 subjacent clays can take place. 



Similar Occurrences in the same Region 



In a paper entitled " L'Eboulis de Saint Alban," * Monseigneur Laflamme has 

 given an excellent account of a landslip that occurred on April 27, 1S94, on the 

 Sainte Anne river, distant about 7 miles only from that above described and af- 

 fecting similar deposits of the same plain, although at Saint Alban a large part of 

 the slide consisted of the Saxicava sands, there developed in great thickness above 

 the Leda cla}^ 



The landslip at Saint Alban was also much larger than that on the Blanche, an 

 area more than 3 miles in length along the river and about 7,700 feet in greatest 

 width having moved bodily down into the valley. Five or six farm-houses were 

 destroyed or swallowed up, four lives were lost, and the entire mass of the slide is 

 estimated at from 600,000,000 to 700,000,000 cubic feet. 



The landslip at Saint Alban was also different in its cause and character. The 

 river was first dammed by a comparatively small slide, and when the water thus 

 held back eventually broke through, its undermining action on the high banks 

 of the valley was such as to precipitate the collapse of the much greater area above 

 noted, t 



A brief description of a landslip almost identical in character with that of the 

 Blanche and affecting a similarly situated part of the same Saint Lawrence plain 

 has, however, previously been given by Sir William Logan in a paper read before 

 the Geological Society of London in 1842. | 



This landslip occurred on the Maskinonge river, about 50 miles to the southwest 

 of the Riviere Blanche, on April 4, 1840, and was examined by Logan in the follow- 

 ing autumn. Like that on the Blanche, its outlet through the bank of the valley 

 was narrow, and its greatest width, about 600 yards, occurred at some distance 

 back from this bank. The length of the collapsed area was 1,300 yards, and its 

 area about 84 acres, the depth of the depression being about 30 feet. The nearly 

 liquid clay flowed both up and down the valley of the Maskinonge for a distance 

 of about three-quarters of a mile in each direction, bearing with it large blocks and 

 masses of unbroken clay. The whole movement was effected in about 3 hours, 

 the first mass of clay detached being about 200 yards in width by 700 in length. 



* Transactions Royal Society of Canada, vol. xii, part iv, 1894, p. 63. 



t Since the present paper was read a short note by the same author on the Blanche landslip has 

 been published in the Report of the Commissioner of Colonization and Mines of Quebec for 1898, 

 p. 131. 



t Proceedings of the Geological Society of London, vol. iii, p. 767; also Life of Sir William 

 Logan, p. 95. 



LXIX— Bull. Geol. Soc. Am., Vol. 10, 1898 



