July 5, 1894J 



NATURE 



•00 



lion. Finally, the enormous pile of rubbish, weighing quite 

 800,000,000 tons and lying in a valley nearly one mile wide, 

 would, if shifted, become jammed into a gorge only 500 feet 

 wide. 



Mr. Holland traces several causes, which were some time 

 conspiring to the one end of bringing about the catastrophe 

 that has been attended with such serious consequences at 

 Gohna. 



Among these the principal, or more correctly, the one which 

 gave facilities for the action of all the others, is the dip of 

 the strata towards the gorge. Over Gohna village, the dip of 

 the dolomites in the southeast direction increases, until in 

 Marthana itself the beds are inclined in the face of the cliff at 

 an angle of about 45''-50°, and consequently large platey 

 surfaces are exposed by the fall. As the dip of the rocks is 

 greater than the angle of repose of dolomite or shale-slabs, 

 sliding would naturally take place when necessary facilities are 



pendicular clifF is safe on the south side in which direction the 

 rocks dip, there is a perpetual slipping on the north side, and 

 no slope greater than the angle of repose of the loose blocks 

 would be safe. 



In the landslip at Gohna not only was the support removed 

 by undermining at the foot of the slope, and loosening of the 

 beds, but the beds were impelled outwards by a series of changes 

 following as a natural consequence of the processes which 

 destroyed the originally compact nature of the strata. These 

 causes combined, taking advantage of the stratigraphical 

 facilities, precipitated the mass of material which now dams 

 back the Birahi Ganga. They are as follows : — 



(I) Tlwse producing a hoiening of the slrala. 

 (a) Dolomitisation. 

 \fi) Solution by atmospheric waters, 

 (r) Reduction of coefficient of friction by water. 



Fig. T. View of Gohna Tal from the edge of the Dam, 190 feet below overdow point. Tir^ul (23,406 feet) anil two associated peaks (over 20,000 feet) 



form the background 



presented. .So long as the slope of the surface does not exceed 

 in angle the dip of the strata there is no danger of a slip ; but 

 when, as in this case, the foot of the slope is undermined by 

 the action of a river and by springs, the average slope of the 

 surface is increased, and there is a tendency for the beds lying 

 between the line of slope and the line of dip to slide off. 



It is pointed out that the influence of the dip of the 

 strata in fashioning the surface slope is well illustrated in 

 the Cheddar Valley. The river has cut a gorge approxi- 

 mately in the direction of the strike of the carboniferous 

 limestone, which dn)s on both sides of the river at an angle 

 of ls°-24° south. The south side of the gorge is an almost 

 perpendicular cliff 400 feet high, whilst on the north side 

 the slope is only slightly greater than the dip of the beds, 

 which are constantly, though gradually, slipping down as the 

 river is deepening its valley. Thus, whilst an almost per- 



NO. 1288, VOL. 50] 



(2) Subsequent changes impelling Urata in the direction pj 

 least resistance. 



{a) Expansion of products on oxidation and hydration. 

 (/<) Changes of temperature, 

 (c) Hydrostatic pressure. 



Mr. Holland describes the action of each of these causes, 

 and concludes his report by pointing out that owing to the fact 

 that the folding of the Himalayan range has continued to times 

 geologically recent, if not still in action, there has resulted a 

 condition of strain frequently manifcbting and lelieving itself by 

 earthquakes, and of s'.eep slopes with rushing torrents, 

 frequently resulting in landslijis. When subsequently the 

 inequalities of level have been sufliciently reduced by denuda- 

 tion, the slopes will be more stable, rivers less violent, and the 

 scenery tamer — a condition of affairs exemplified by the more 



