o 13 B. KOTO: CAUSE OF THE (iTîEAT 



often (lone. Thov inv renlly connected with underuTound structure and 

 are due io displacement of tlie rock-masses whieli constitute the 

 external ciaist of the earth. They therelore (vcur where there exists 

 a discontinuity of rocks, and the earth-rent which we have descrihed, 

 and which is the mtiin ])oint in the present pa])er, must l)e regarded 

 as an exam]>Ie. 



Tills rail (il iJw surface ioi»]; mull ij'drioiis forms. When traversing 

 a ridge of mountain^ or a spur of hills, it caused extensive landslips, 

 one side of it descending considerahly in level, carrying the forest 

 with it, l)ut with the trees com}>licated1y interhx-ked or prostrate on 

 the ground, as on the ridge of Ilaku-san. On flat ground it 

 sometimes created a terrace of »about G metres in height, as in Midoi-i 

 (PI. XXXn .), somewhat like a railway embankment seen from afar. 

 When the vertical displacement was not very consider:d)le, the earth- 

 rent left a mark on the gi-ound, rcsrmhlimj rciij much ihr patluraij of a 

 (liijiitttic molr or the trade of a ploinili-sliarc (PI. XXXY.). 



The manner in whi<-h this peculiar low mound was formed may 

 be ex])lained l\y reference to a monoclin:d flexure — a geological struc- 

 ture Avell exhibited on a grand scale in the L'lateau of Wahsatch.'* 8u]> 

 pose the iiat l)ott(^m of a vaHey like the Xeo, filled up with soil and 

 gravel which rest unc<3nfoi'mably upon tlie hard mass of the older 

 rocks, and form their -cover,' and tliat the basement should give way 

 by faulting along the ATrtical thrust-plane ; there a certain ])ortion 

 of the uncompressed 'cover' will tliere1)y be uplifted, so as to 

 form a rounded ridge of earth by the lateral compression of a sub- 

 jacent mass along the line of discontinuity. In this w^ay a mono- 

 clinal flexure in the loose superficial covering, which aj^pears in section 

 as a flexure connectinii- two horizontal b;n-s of strata, would be 



* C. E. Button, liqmrt on the Genlnrj]i of tlw Hifih Plotefiiist of Utah, p. 25-51-. 



