Two small veins of the same kind, only two or three feet wide, may be seen in the bed of the Water of Leith, traversing the horizontal strata, the one is above St Bernard’s well, the other immediately below it.  But, more particularly, in the shire of Ayr, to the north of Irvine, there are to be seen upon the coast, between that and Scarmorly, in the space of about twenty miles, more than twenty or thirty such dykes (as they are called) of whin-stone.  Some of them are of a great thickness; and, in some places, there is perceived a short one, running at right angles, and communicating with other two that run parallel.

There is in this country, and in Derbyshire[14], another regular appearance of this stone, which Cronstedt has not mentioned.  In this case, the strata are not broken in order to have the whin-stone introduced, they are separated, and the whin-stone is interjected in form of strata, having various degrees of regularity, and being of different thickness.  On the south side of Edinburgh, I have seen, in little more than the space of a mile from east to west, nine or ten masses of whin-stone interjected among the strata.  These masses of whin-stone are from three or four to an hundred feet thick, running parallel in planes inclined to the horizon, and forming with it an angle of about twenty or thirty degrees, as may be seen at all times in the hill of Salisbury Craggs.

[Note 14:  See Mr Whitehurst’s Theory of the Earth.]

Having thus described these masses, which have flowed by means of heat among the strata of the globe, strata which had been formed by subsidence at the bottom of the sea, it will now be proper to examine the difference that subsists between these subterraneous lavas, as they may be termed, and the analogous bodies which are proper lavas, in having issued out of a volcano.[15]

[Note 15:  The Chevalier de Dolomieu, in his accurate examination of Aetna and the Lipari islands, has very well observed the distinction of these two different species of lavas; but without seeming to know the principle upon which this essential difference depends.  No bias of system, therefore, can here be supposed as perverting the Chevalier’s view, in taking those observations; and these are interesting to the present theory, as corresponding perfectly with the facts from whence it has been formed.  It will be proper to give the account of these in his own words.

La zeolite est tres-commune dans certains laves de l’Ethna; il seroit peut-etre possible d’y en rencontrer des morceaux aussi gros que ceux que fournit l’isle de Ferroe.  Quoique cette substance semble ici appartenir aux laves, je ne dirai cependant point que toutes les zeolites soient volcaniques, ou unies a des matieres volcaniques; celles que l’on trouve en Allemagne sont, dit-on, dans des circonstances differentes; mais je doit annoncer que je n’ai trouve cette substance en Sicile, que dans les seules laves qui evidemment ont coule dans la mer, et qui