248 Notes on the Recent Earthquakes [No. 123. 



the duration was one minute and the velocity 1 .44 miles per minute, the 

 breadth was 1 .44 miles. 



Whence we have, Miles. 



Breadth of zone of disturbance at Kawulsur, 75.71 

 >, „ ,, at Poojnah 7.00 



„ „ at Kulsea, 1.44 



Whatever may be the effective cause of Earthquakes, whether modu- 

 latory motion communicated to internal masses of fluid matter, and 

 from thence communicated to the super-imposed crust of the earth, or 

 vibrations propagated from foci of disturbance through the solid crust 

 itself, or a combination, as some facts would intimate of both these 

 causes, there are two modes in which we may conceive these motions 

 to be spread abroad. First, they may proceed in gradually enlarging 

 circles, (as when a stone is thrown into water,) the focus of disturbance 

 being the common centre ; or they may be propagated along a distinct 

 and defined track, (as when a string or wire is seized at one extremity 

 and motion communicated to the whole from this,) when the focus of 

 disturbance would be at one end. In the first case we would expect 

 the effects of the Earthquake to be felt at points equi-distant from the 

 centre at times approximating, but not exactly coincident both with each 

 other, as the rate of progress of the undulations would necessarily be 

 affected by the nature of the rocky crust through which they were pro- 

 pagated. In the second case, we would expect, that while the effects 

 of the shock were more or less severe within certain limits, beyond 

 these limits none would be experienced. All the information I have 

 been able to collect tends to shew, that the Earthquake of the 1 9th Fe- 

 bruary 1842, belonged to this latter class, and if lines be drawn through 

 Peshawur, Ferozepore, &c. with parallels through Jellalabad, which as 

 yet forms the southern limit of the track, it will be found that the 

 breadth of the district affected by the shock was somewhere about 40 

 miles, and in it are included the mountain ranges to the south, east, 

 and west of Peshawur, with a considerable portion of what has been 

 called the Salt range. This estimate has been formed solely from the 

 facts collected by myself, and it may yet require to be much modified 

 as our information extends. The method of what may be called the 

 linear, in contradistinction to the circular propagations of Earthquake 

 shocks, appears to me to lead very distinctly to the conclusion, that in 



