THEORY of the EARTH. 279 



the coaft, between that and Scarmorly, in the fpace of about 

 twenty miles, more than twenty or thirty fuch dykes (as they 

 are called) of whinftone. Some of them are of a great thick- 

 nefs ; and, in fome places, there is perceived a fhort one, run- 

 ning at right angles, and communicating with other two that 

 run parallel. 



THERE is in this country, and in Derbyshire *, another re- 

 gular appearance of this ftone, which CRONSTEDT has not 

 mentioned. In this cafe, the flrata are not broken in order to 

 have the whinflone introduced, they are feparated, and the 

 whinftone is interjected in form of ftrata, having various de- 

 grees of regularity, and being of different thicknefs. On the 

 fouth fide of Edinburgh, I have feen, in little more than the 

 ipace of a mile from eaft to weft, nine or ten mafles of whin- 

 ftone interjected among the ftrata. Thefe mafles of whinftone 

 are from three or four to an hundred feet thick, running pa- 

 rallel in planes inclined to the horizon, and forming with it an 

 angle of about twenty or thirty degrees, as may be feen at all 

 times in the hill of Salifbury Craggs. 



HAVING thus defcribed thefe mafles, which have flowed by 

 means of heat among the ftrata of the globe, ftrata which had 

 been formed by fubfidence at the bottom of the fea, it will 

 now be proper to examine the difference that fubfifts between 

 thefe fubterraneous lavas, as they may be termed, and the ana- 

 logous bodies, which are proper lavas, in having iflued out of a 

 volcano f. ^ 



THERE 



* See Mr WHITEHURST'S Theory of the Earth. 



(- The Chevalier de Dolomieu, in his accurate examination of ./Etna and the Lipari 

 iflands, has very well obferved the diftindion of thefe two different fpecies of lavas ; but 

 without feeming to know the principle upon which this eflential difference depends. No 

 bias of fyfiem, therefore, can here be fuppofed as perverting the Chevalier's view, in 

 taking thofe obfervations ; and thefe are interefting to the prefent theory, as correfpond- 

 ing perfectly with the fads from whence it has been formed. It will be proper to give- 

 the ap count of thefe in his own words. 



LA 



