and especiallj/ in Scotland. ^8^ 



by occurring on the same day^ which allows, generally speaking, 

 a difference of nearly twenty-four hours between them. As 

 long as there is such vagueness in the data, it is impossible to 

 draw any conclusion. Indeed, it may be affirmed, that until 

 registers are kept in those districts which are known to be 

 particularly subject to earthquake-shocks (as there now are at 

 Comrie in Perthshire, and at St Jean de Mauricnno), so as to 

 fix not merely the day, but the hour and minute of their oc- 

 currence, with other particulars, it will be impossible to say 

 whether the sources of volcanic action in this country and in 

 other countries are connected. 



5. The localities in this country, which are most subject to 

 Earthquake- Shocks, are charactei'izedhy certain geological fea- 

 tures. 



It has been mentioned that nearly two-thirds of the shocks 

 felt in Scotland occur in the district of Stratherne, and par- 

 ticularly in the neighbourhood of Comrie ; and that a large 

 proportion issue from the Great Glen of Scotland. Now, along 

 these districts, it is well known that there are deep and ex- 

 tensive fissures and dislocations in the earth's crust ; and, more- 

 over, that there is an extensive development of granite and 

 ancient porphyry rocks, which are generally thought to have 

 their foundations deeply laid in the interior of our planet. 

 Through Stratherne, the author has lately traced seven or eight 

 basaltic dykes, filling up ancient fissures, which are all parallel 

 to one another, and run in a direction nearly, if not exactly, co- 

 incident with the adjoining range of the Grampians. These 

 dykes have been traced for about 50 miles, exhibiting in that 

 long course little or no variation in quality, thickness, or di- 

 rection, and they therefore attest the magnitude of the scale 

 on which the disrupting forces had operated. Though proof 

 of a like special character cannot be yet offered of dislocations 

 along the Great Glen of Scotland, yet it may be generally 

 affirmed of every district abounding in granite and porphyry, 

 as is the case in the Great Glen, and particularly along its 

 north side and at its west extremity (where the shocks have 

 been most frequent), that great disturbance must have been 

 produced by the outburst of these igneous rocks ; and, in 

 fact, it is generally admitted that the whole slate- series of the 



