SLIPS ON THE ILLAWAKRA RAILWAY AT ST AN WELL PARK. 59 



line passes through a succession of spurs of rotten shales and drift 

 composed of sandstone boulders mixed with decomposed shale and 

 pipe-clay, the shale is cut up in all directions with pipe-clay veins. 

 During the construction of the line the contractors experienced 

 considerable trouble with slips in the cuttings, and the completion 

 of the line was delayed in consequence. After the line was opened 

 the year 1888 being a tolerably dry year no very serious trouble 

 was experienced ; but when the great rain storm of May the 25th, 

 26th, and 27th, 1889 set in, during which over 20 inches of rain 

 fell, the. results were most serious. On Monday the 27th of May 

 the cutting under Mr. Hargrave's house came in and completely" 

 blocked the line, several feet of earth and mud being forced over 

 the rails, and the embankment at 33 miles slipped out bodily from 

 the bed rock, leaving the ends of the sleepers over-hanging about 

 4 feet. Every effort was made to clear the road and the traffic was- 

 resumed on Friday 31st May, but it was found that the bank at 

 33 miles which had been temporarily repaired with ashes &c, was 

 still travelling seaward at a serious rate. It was necessary to 

 bring a constant .supply of ashes to lift the road to keep the traffic 

 going, large quantities of the soil were continually going over the 

 cliff as the ground settled down, the whole space between the foot 

 of the railway embankment and the edge of the cliff being broken 

 up into large fissures. 



The problem that then had to be considered was how to stop 

 the outward motion of the ground since it was evident that unless 

 this was stopped there was every probability of the hill above the 

 line following, as it is composed of drift, and from its appearance 

 was nothing but an old natural slip. If this had taken place the 

 line would have been blocked for months, and a deviation in the 

 shape of a tunnel would have been necessary to get out of the 

 broken ground. 



After carefully examining the ground the author came to the 

 conclusion that the only chance of saving the embankment was. 

 by an extensive system of drainage, and thus if possible to con- 

 solidate the ground above the bed rock, the great depth of the soil, 

 and the enormous mass of material to be kept back making it 

 almost impossible to do any good with retaining walls. Before 

 describing the system adopted in connection with the drainage 

 works, it may be well to describe the nature of the ground so that 

 the difficulties of the work may be better understood. The cliff 

 which at this place is about 150 feet above sea level, is of sand- 

 stone with beds of shale. The surface soil which varied from about 

 1 to 30 feet in thickness rested on a bed of chocolate coloured 

 shale with numerous veins of pipe clay, the dip of the strata being 

 slightly inclined inwards, thus giving a slight recess at every 

 break of the strata to hold the water, and keep the surface soil 



