336 



The Ohio Journal of Science [Vol. XX, No. 8, 



GEOLOGICAL STRUCTURE FAVORABLE FOR LANDSLIDES. 



An examination of the geological structure of the area where 

 the slide occurred reveals conditions favorable for the develop- 

 ment of the conditions of unstable equilibrium prerequisite to 

 landslides. Massive lava flows several hundred feet thick have 

 been poured out on a platform of sandstone dipping away from 

 the vents. The strata are bent up against the volcanoes all 

 around, as though they had been blistered up by the injection 

 of a laccolith beneath. 



Photograph by D. B. Church 



DETAIL AT THE EDGE OF THE MIDDLE SECTION OF THE SLIDE. 



The man at the right gives the scale. The mountain side was deeply plowed up 



by the flying rocks. Note the absence of any marginal ridge and 



the high percentage of solid rock in the detritus. 



The lava flowing down the inclined surface of the sandstone 

 often congealed before reaching the bottom. As it hardened, 

 joint planes perpendicular to the sloping surface developed, 

 changing the solid flow, to a certain extent, into a series of slant- 

 ing columns. Closely adjacent to the part of the cliff that fell 

 away, colossal columns are still standing, apparently so ready 

 to topple over that the marvel is that they survived the shock 

 which set off their neighbors. (See page 349). 



Through the joint cracks water doubtless reached the 

 original surface and, working along, may have greatly facilitated 

 movement by lubricating a bed for the unstable mass above. 



