Seay Been TF ay. a hn 
“ty Se ee es Mave 
wae Yay rs we? Nie 
Ba ee Se 
z ‘ We nae od 
> ona 
358 DYNAMICAL GEOLOGY. —*[Boox TIL. ~ 
rapid than that of the lower cliff (g) washed by the sea.* In the 
year 1839, after a season of wet weather, a mass of chalk on the 
same coast slipped over a bed of clay into the sea, leaving a rent 
three-quarters of a mile long, 150 feet deep, and 240 feet wide. 
The shifted mass, bearing with it houses, roads, and fields, was 
eracked, broken, and tilted in various directions, and was thus 
prepared for further attack and removal by the waves.? Of the 
antiquity of many landslips interesting proof is supplied by the 
ancient buildings occasionally to be seen upon the fallen masses. 
There would seem in these cases to have been comparatively little 
alteration of the scenery for many centuries. The undercliff of the 
Isle of Wight, the cliffs west of Brandon Head, county Kerry, the 
basalt escarpments of Antrim, and the edges of the great volcanic 
plateau of Mull, Skye, and Raasay, furnish illustrations of such old 
and prehistoric landslips. 
On a more imposing scale, and interesting from its melancholy 
circumstances being so well known, was the celebrated fall of the 
Rossberg, a mountain (a, Fig. 105) situated behind the Righi in 
‘ Switzerland, rising toa height of more than 
bee 5000 feet above the sea. After the rainy 
c- 1-5 summer of 1806, a large part of one side 
of the mountain, consisting of steeply 
sloping beds of hard red sandstone and 
conglomerate (6), resting upon soft sandy 
Be eee ee eno c), gave way. The lubrication 
THE FALL OF THE MOSSBERG. of the lower surface by the water haying 
loosened the cohesion of the overlying mass, thousands of tons of 
solid rock, set loose by mere gravitation, suddenly swept across the 
valley of Goldau (d), burying about a square German mile of fertile 
land, four villages containing 330 cottages and outhouses, with 457. 
inhabitants.2 In 1855 a mass of débris, 3500 feet long, 1000 feet 
wide, and 600 feet high, slid into the valley of the Tiber, which, 
dammed back by the obstruction, overflowed the village of San 
Stefano to a depth of 50 feet, until drained off by a tunnel. 

§ 3. Brooks and Rivers. 
These will be considered under four aspects :—(1) their sources of 
supply, (2) their discharge, (3) their flow, and (4) their geological 
action. 
I. Sources of Supply.—Rivers, as the natural drains of a land 
surface, carry out to sea the surplus water after evaporation, together _ 
with a vast amount of material worn off the land. Their liquid 
1 De la Beeche “ Geol. Observer,” p. 22. 
2 Conybeare and Buckland’s Axmouth Landslip, London, 1840. Lyell, “ Principles,” 
i. p. 536. 
Yi Zay, “Goldau und seine Gegend.” A small landslip took place at the samo 
locality in August, 1874. Baltzer, Newes Jahrb. 1875, p. 15. Upwards of 150 destructive 
landslips have been chronicled in Switzerland, [ied], Newes Jahrb. 1877, p. 916. 
