316 ON LANDSLIPS. 



brook, which is liable to sudden floods. When the con- 

 tractor had got out the ground for the foundation of this 

 culvert, the 'bottom was so bad that he did not know what 

 to do. On inspection I found that the bottom was in lias 

 slip-clay, in which the feet sank ankle-deep at every step ; 

 so I had a trial pit sunk near it, and found that the same 

 stufi* went down for 30 feet. The question was, How could 

 a culvert be built upon that bottom to carry the load of a 

 52-ft. bank ? I felt it to be a serious, momentous, and ner- 

 vous question ; for if that culvert should collapse after the 

 bank had been made, it would of coarse be after heavy rains 

 when it would be running nearly full of water. The heavy 

 bank would follow the arch and choke the culvert. This big 

 bank might in this way form a great dam across the valley, 

 against which the water would rise, making a great reservoir 

 of the valley above, until such time as it had accumulated 

 sufficient force to cut itself a passage through the upper part 

 of the bank. And this passage, though small at first, having 

 once been made, it would very rapidly scour, until the water 

 in a great body w^ould burst through (as in the Holmfirth 

 reservoir), and suddenly discharge a great flood, through the 

 centre of Bristol, into the Floating Harbour ! — for the brook 

 runs into the Frome at Baptist Mills. 



The facts to be considered were these : The valley bottom 

 is narrow, and the sides rise, on either hand, at as steep a 

 slope as the lias subsoil will allow. The railway crosses this 

 valley very much askew, so that the culvert w^as a very long- 

 one, and had to be founded upon that soft slip-clay. But 

 though the clay would slij^ in any available direction under 

 such a load, I had ascertained that there was no compressible 

 material, such as peat, mixed with it. 



After thinking it over, I decided to build the culvert upon 

 the bad bottom as it was, only cov^ering it with a coating of 



