540 Dr. C. Dan'soii — British Earthqiialiea. 



isoseismal ; and the sound was also heard, but no shock felt, at 

 Dennington, one mile north-west, and Earl Soham, 3 miles west, 

 of the same curve. The centre of the isoseismal is situated at 

 a point one mile south-west of Svvefling and 15 miles north-east 

 of Ipswich. 



There was a sudden shock followed by a brief tremulous move- 

 ment, lasting for a few seconds. The sound was heard by all 

 observers, three of whom compared it to passing waggons, etc., 

 one to thunder, one to the fall of a building, three to tlie fall of 

 a heavy body, and six to explosions or the firing of a heavy gun. 

 Thus, 9 out of 14 observers make use of types which are of short 

 duration. 



Framlingham Earth-shaJce : Oct. 22, 1901. — Time of occurrence, 

 about 9.15 a.m.; intensity, 4; centi'e of isoseismal 4 in lat. 

 52° 12-7' N., long. 1° 15-2' E. ; number of records, 22, from 13 

 places, and 27 negative records from 23 places. 



With two exceptions, the shock was felt within an area of the 

 same dimensions, and almost exactly the same position, as in the 

 former earth-shake. The shock and sound were noticed at Earl 

 Soham, 3 miles west of the isoseismal 4; the shock was also felt 

 at Snape, one mile to the south-east, and the sound was heard at 

 Cretingham, 3^ miles to the west. 



The shock was similar to that of the first earth-shake, consisting 

 of one prominent vibration followed by a tremulous motion, and 

 lasting altogether about 3 seconds. The soimd was heard by 18 

 out of 20 observers, and was compared to thunder in 2 cases, to 

 the fall of a heavy body in 7, and to explosions or the firing of 

 heavy guns in 8 cases ; 15 out of 17 comparisons being to types of 

 short duration. 



Origin of the Earth-sliakes. — While I am unable to point to any 

 definite disturbances as the cause of the earth-shakes, their seismic 

 origin seems to me doubtful for the following reasons : — 



(1) The shock was a sudden disturbance followed by a brief 

 tremulous motion. 



(2) The sound was compared by nearly half the observers to 

 that of an explosion or the firing of a heavy gun, and by more than 

 tliree-quarters to types of brief duration. 



(3) While inquiries were made throughout the surrounding 

 district, the places from which negative records come are, with 

 one exception in each case, absent from the south-east of the 

 disturbed area. 



These conditions seem to me to point to the firing of a moderately 

 heavy gun some distance to the south-east, probably in the neigh- 

 bourhood of Orford Ness, which is 14 miles S.E. of Framlingham. 

 The shock and sound are such as would be so produced ; and, in 

 the immediate neighbourhood, would be assigned at once to their 

 true cause. It is only at a distance of some miles from the origin 

 that they begin to lead to the suspected occurrence of an earthquake. 

 From the intermediate region it is usually difficult in such cases to 

 obtain any records, either descriptive or negative. It is known that 



