C. Davison — The Ex moor Earthquake. 



555 



instantaneous bumps ; a sound, as of a heavy cart-load of iron 

 crossing a wooden floor, grew and died away with the trembling, 

 encountering, as it were, two large stones on the way at the instants 

 when the bumps were felt. At Challacombe two distinct rumbles 

 were heard by one observer, without any interval between, each 

 increasing in intensity and then dying away, the first and louder 

 lasting three or four seconds, the second rather less. Lastly, at 

 Holland two rumbles (like distant thunder or firing of artillery) 

 were heard, but in this case there was an interval of a few seconds 

 between them, and it was during this interval that the only 

 perceptible movement was felt. 



Disturbed Area and Isoseismal Lines. — The two curves on the map 

 represent the isoseismals of intensities iv and in respectivel}', the 

 latter forming the boundary of the disturbed area. The isoseismal 

 in is 29£ miles long, 16^ miles broad, and contains 389 square 

 miles. The length of the isoseismal iv is 22f miles, its breadth 

 12^- miles, and the area included within it 228 square miles. Both 

 curves are elongated ellipses, and their longer axes are parallel, 

 being directed W. 22° N. and E. 22° S. If the earthquake were 

 due to fault-slipping, this must, therefore, be the direction of the 

 fault-line in the neighbourhood of the epicentre. 



Map of the Exmoor Earthquake of Jan. 23, 1894. ! 

 The distance between the two isoseismals being 1| miles on the 

 north side of the longer axis, and 3 miles on the south, it follows 



1 The places where the shock was felt are shown by small black discs ; a cross 

 drawn through the disc means that the sound was also heard ; a cross alone, that the 

 souud was heard, no reference in the account being made to any perceptible vibra- 

 tion ; a small circle marks the places where the earthquake was not observed ; and 

 a cross drawn through a circle, a place where the sound was heard, but no shock was 

 felt. 



