348 The Ohio Joiinial of Science [Vol. XX, No. 8, 



The slope of the bed down which the slide coursed is of the 

 form most favorable to reducing friction and so assisting the 

 motion, for it approximates Shiele's Tractrix, or "Antifriction 

 Curve," such as is used in a toboggan slide. As in a toboggan 

 slide, starting with a nearly perpendicular drop and gradually 

 changing into an inclined plane of ever decreasing pitch whose 

 friction absorbs the acceleration due to gravity and keeps the 

 toboggan moving at a nearly constant rate to the end of its 

 course, so in the Mageik Slide there was first an almost vertical 

 drop of 750 feet, then half a mile of steep hillside, followed by a 

 flat valley of gradually decreasing grade until in the last mile 

 the descent was only about 200 feet. It is thus evident that, 

 aside from the bend in its course, the form of its bed was such 

 as to offer a minimum of resistance to its movement. 



COMPARISON WITH OTHER LANDSLIDES. 



The dimensions of the Elm Landslide as given above were: 

 Average fall 450 meters, length 1500 meters, area 900,000 

 square meters, depth 10-20 meters, volume 10,000,000 cubic 

 meters. 



The Frank Slide covered 1.03 square miles, to an average 

 depth of 15 yards. The amount of material moved is estimated 

 at 36,000,000 cubic yards.f 



The Rossberg Slide is said to have been 4300 yards long, 



349 wide, 35 deep, and to have totalled 51,000,000 cubic yards. | 

 The Colorado landslides are especially notable because of the 



great number that have occurred in a restricted area in the 

 vicinity of Silverton. The largest single area covered with 

 landslide material is Silver Mountain Landslide, which covers 

 ten square miles, being therefore considerably larger than the 

 Mageik Slide. But this is believed to be a compound of several 

 slides that occurred at different times. Moreover, it is not 

 of the violent type, but an ordinary landslide which is believed 

 to have been in continuous slow movement for a long time. 

 Of the "Rock Streams" proper, the largest in the Silverton 

 area is somewhat less than a mile long, and therefore very 

 much smaller than the others that have been cited. 



Of the other landslides in our area, two are so large as to 

 deserve notice in this series of comparisons. The Katmai 



tMcConnell, R. G., and Brock, R. W. op. cit. 

 JGoldau und Seine Gegend. Neues Jahrbuch, 1875. 



