LANDSLIDE AT CLEVELAND, OHIO 629 



in the valley. Some of the shales are more thickly bedded, and would not 

 allow seepage like the thinly bedded portions such as the Chagrin, which 

 occurs at the base of the cliff. In this Chagrin are also found several sand- 

 stone layers, which would permit much easier circulation than the shales. 

 Along its course it will perform the usual work of underground water and dis- 

 solve any soluble material, such as the iron sulfate formed by the decomposi- 

 tion of the pyrite and marcasite, which are always present in these shales in 

 variable quantities. The breaking up of these substances may also cause the 

 formation of free sulfuric acid, which in turn would attack the aluminum sili- 

 cate of the shales, and form alums. This chemical action would, therefore, 

 result in the weakening of those shale layers along which water could circulate. 



Another cause which probably aided in weakening the foundations of the 

 cliff is that up to 6 years ago the stream flowed within 25 feet of the base of 

 the displaced block. The course of the creek was changed at the time the 

 brick plant was erected in order to make their shale bank more accessible. 

 The river in previous times flowing so near the base of the point would 

 undoubtedly have exerted some mechanical and chemical action on the shales. 

 This old waterway, although filled up, would serve as a better drainage 

 channel than if it were solid shale. 



Still another factor which might aid in rock disintegration at this point is 

 the fact that at the time the creek was changed a sewer was built along the 

 front of the cliff about 7 feet below the kiln floor and nearer the cliff than the 

 former stream course. This excavation was filled up with loose material, 

 which would make a channel of porous character along which water could 

 circulate with ease and exert more or less destructive effect on the shale 

 foundations of the cliff. This waterway would give the waters coming down- 

 ward through the joint planes of the bank a quicker circulation, and thereby 

 enable them to perform their work of chemical disintegration at a faster rate. 



The normal weathering action of rain and frost would be expected to exert 

 some effect on the shales, and this action would be greatest on the outside of 

 the cliff, and probably more prominent at the bottom of the same, where the 

 amount of water would be greater. It is to be noted that the axis of the 

 flexure runs along in front of the face of the cliff, where the shales have been 

 longest exposed to the weather and other disintegrating agents. 



Blasting of the shale in the amphitheater to the northeast of the slide occurs 

 quite frequently, and it seems possible that the continued concussions might 

 even fracture the adjacent shales. It certainly would tend to loosen the joint 

 blocks of any rocks in the immediate vicinity. 



It seems plausible that any one, but more probably all of these factors com- 

 bined, may have weakened the shale layers at the bottom of the cliff to such 

 an extent that the simple weight of the mass would tend to cause the outward 

 face to settle on its base. The direct cause of the sinking might well be the 

 dynamite blasts. As a result of the settling, tension would be produced in the 

 strata for some distance into the valley wall. This would ultimately result In 

 the formation of a crack and the separation of the point from the rest of the 

 bank. In this case it was comparatively easy for the rupture to form on 

 account of the weathered joint planes, especially the large one in the Chagrin 

 formation, which measured 95 feet long and 14 feet high and must have 

 exerted considerable influence on the position of the fissure. Immediately 

 following the formation of the crevice, the block would be resting on a plane 



