-'•38 DE. CHARLES DAVISON ON THE [^ ll &- 1 9°4' 



to miscellaneous types. These approximate closely to the pro- 

 portions prevalent in strong earthquakes, the average percentages 

 for the different types in ten recent earthquakes being 46, 22, 10, 

 4, 3, 8, and 6, respectively. The percentage of comparisons to 

 passing traction-engines is 42 within the isoseismal 7 ; 49 between 

 the isoseismals 7 and (3 ; and 50 between the isoseismals 6 and 5. 

 For thunder, the corresponding percentages are 30, 30, and 24 ; and, 

 for wind. 3, 6, and 8 : showing how the sound tends to become 

 smoother and more monotonous with increasing distance from the 

 epicentre. 



The beginning of the sound preceded that of the shock in 62 per 

 cent, of the records, coincided with it in 36, and followed it in 2, 

 per cent. The end of the sound preceded that of the shock in 

 8 per cent., coincided with it in 49, and followed it in 43 per cent., 

 of the records. The duration of the sound was greater than that 

 of the shock in 65 per cent., equal to it in 35, and less than it in 

 1 per cent., of the records. 



Miscellaneous Phenomena. 



A few observations were made in slate-quarries in which the 

 workings are continued underground. At Xantlle, the shock was 

 felt at a depth of from 50 to 70 yards, the workmen thinking 

 that a large fall of rock had taken place. It was also noticed in 

 underground workings at Blaenau Ffestiniog, 19 miles from the 

 centre. 



Among the most interesting observations on the earthquake were 

 those made on the movement of the loose material of screes. Owing 

 to the very gradual creeping downwards with every change of 

 temperature of all stones free to move, a large part of the material 

 is almost in unstable equilibrium, and a very slight force is necessary 

 to set it in motion. 1 At the time of the earthquake, Mr. W. (j. 

 Fearnsides, F.U.S., was sitting on a slope of screes 150 yards south 

 of Lleyn dur Arddu and 1 mile north-west of the summit of Snowdon. 

 There were, he says, three chief shocks within about 14 minutes. 

 The second and strongest so affected the screes that, on turning 

 round, he saw numbers of stones shuffling and rolling down the 

 surface. Stones of all sizes were involved, blocks of felsite up to 2 feet 

 in diameter among them, the larger moving more quickly than the 

 others, and the noise caused during their motion was so great that 

 it finally drowned the rumbling of the earthquake. The screes 

 continued unstable for five minutes, and, at the end of that time, 

 hundreds of newly-fallen blocks were to be seen lying at the 

 base. 2 



1 Quart. Journ. Geol. 8oc. vol. xliv (1888) pp. 232-37, 825-26. 



- A somewhat similar observation was made at Blaenau Ffestiniog, where 

 fragments of slate were seen rolling down the ' tips ; of waste slate from the 

 quarry-workings. 



