Vol. 56.] THE COEKCSH EAETHQTJAKES OF 1898. 3 



gollen, and St. Stythians ; while at 8 other places ifc is stated that 

 neither shock nor sound was observed. 



The boundary of the disturbed area is indicated on the accom- 

 panying map (p. 2) by the broken-and-dotted line. It is 10| miles 

 long, 9 miles broad, and contains 74 square miles. This curve being 

 so nearly circular, it is useless to give the appearance of precision to 

 any estimate of the direction of its longer axis; but that it is approxi- 

 mately parallel to the axes of the isoseismal lines of the principal 

 earthquake is obvious from the map. The centre of the area is 

 1 J miles E. 8° 8. of Wendron. 



The earthquake consisted of two distinct shocks, the first of which 

 occurred at about 10.25 p.m., but probably a little before, and the 

 second about five minutes later. The intensity (according to the 

 Rossi-Eorel scale) was 4 at Helston, and less than 4 at Crowan, 

 llawnan Smith, and Nancegollen. 



The sound was heard at every place where the shock was felt, with 

 the exception of Mabe, from which I have received no information 

 on this point. At each it was compared to the low rumble of distant 

 thunder, but at Helston the sound accompanying the second part of 

 the shock was more like the discharge of distant artillery. 



Earthquake of April 1st, 9.55 p.m. 



This shock, though its intensity in no place exceeded 4, was the 

 strongest of the series, and was much more widely observed than 

 the preceding. The following account is based on 89 records from 

 56 different places. There are also 14 places close to the boundary 

 of the disturbed area where the earthquake, so far as known, was 

 not perceived. 1 



Isoseismal Lines and Disturbed Area. — The isoseismal 4 

 is 13 miles long, 7 \ miles broad, and contains 76 square miles. Its 

 longer axis is directed E. 33° ~N. and W. 33° S. The isoseismal 3, 

 which forms the boundary of the disturbed area, is 19 miles long, 

 12 miles broad, and 175 square miles in area, its longer axis running 

 E. 32° N. and W. 32° S. The distance between the isoseismals is 

 1*7 miles on the north-western side and 2*7 miles on the south-eastern 

 side. The centre of the isoseismal 4 is 2 miles east of Wendron. 

 The centre of the disturbed area of the earthquake of March 29th 

 lies almost exactly on the longer axis of the isoseismal 4, and at 

 about a mile on the south-western side from the centre of this curve. 



The forms and relative positions of the isoseismal lines enable us 

 to determine the direction and hade of the originating fault. The 

 average direction of the fault-line must be approximately parallel to 

 the longer axes of the isoseismals, and therefore cannot differ much 

 from E. 33° N. and W. 33° S. The hade of the fault must be to the 

 south-east, as is shown by the greater distance between the isoseismals 

 in that direction than in the opposite one. The exact position of the 



1 With the exception of one curve already mentioned, the accompanying 

 map relates entirely to this earthquake. 



b2 



