630 PROCEEDINGS OF THE BALTIMORE MEETING 



slightly inclined toward the valley. The weight of the mass now has a hori- 

 zontal component in addition to the previous vertical one. which produces 

 motion away from the cliff as well as slightly downward. This might produce 

 sufficient pressure to cause buckling at the base of the block in the valley 

 floor, where the shales are presumably weaker from longer exposure to erosive 

 agents. In this instance it would seem that the vertical component was the 

 more important factor in forming the fold, since there seems to be but little 

 lateral displacement. Professor Charles A. Cadwell has pointed out to the 

 writer the resemblance of this slide to buildings with weak foundations, and 

 believes that the flexure was caused principally by the fact that the center of 

 gravity of the sunken portion is vertically not above the center of the sup- 

 porting base, but rather nearer the valley side. This causes the unit pressure 

 on the valley side of the base to be enormously greater than on the bank side. 

 In testing the supporting power of foundations for proposed buildings, and 

 especially for dams, it is common engineering experience that at so-called 

 "failure" the ground will rise up around the imposed load, flowing out from 

 beneath it. as was reported to be the case with the test loads applied on the 

 site of the State house at Albany. New York. It is also known that clay-like 

 rocks, especially in coal, but also in other mines, sometimes are inclined to 

 "squeeze" at comparatively shallow depths below the surface. The buckling 

 of large timbers in the Michigan iron mines is also quite a common occurrence. 

 It may be objected that such materials are far weaker than shales, and that 

 the latter would require much greater pressures to flex them than those 

 involved in this landslide. However, since these shales have actually buckled. 

 the writer sees no other explanation for the fact than the vertical and to 

 some extent the lateral pressures inherent to the dislocated mass. 



The settling of the mass was not noticed until some time after the buckling. 

 which would indicate that the sinking was caused by the buckling, and again 

 shows the resemblance of this movement of rock to the behavior of building 

 foundations at "failure" where the vertical pressure is the chief factor. 



Relation to Anticlines along Stream Valleys 



Professor H. P. Cushing mentioned to the author the fact that in several 

 instances around Cleveland and elsewhere he had encountered anticlines of 

 local nature in postglacial gorges. One explanation of such flexures has been 

 that they were caused by the vertical pressure of the walls on the valley floor, 

 which relieves the pressure by buckling. It is thought, however, that many of 

 these folds occur where the walls of the valley are not thick enough to produce 

 such a pressure as would seem necessary. With this Cleveland landslide as an 

 object lesson, the writer has come to the conclusion that elsewhere anticlines of 

 local character, especially in shales, may have been produced by landslides 

 similar to the one which is the subject of this paper. 



Other Landslides oe similar Nature 



During the discussion of the above paper at the Baltimore meeting Doctor 

 J. W. Spencer 2 called attention to a landslide which took place April 15, 1884, 



1 A landslide at Brantford. Ontario, illustrating the effects of thrusts upon yielding 

 strata. American Naturalist, 1887. p. 267. 



