88 ON THE CONVOLUTIONS OF STRATA, 



consequence of the congelation of its upper part, that aperture 

 is closed. 



What is true of volcanoes, must be no less true of those 

 internal operations, which, according to the Huttonian theory, 

 have been the means of raising all the rocks and mountains 

 from the bottom of the sea into their present situation ; and 

 by which the unstratified substances have penetrated the stra- 

 ta, and filled the rents formed in them, producing the veins or 

 dikes so common in this country, just as we have seen the 

 lava of Mount Somma filling the rents through the beds of 

 lava and of cinders. 



It cannot be doubted, that the secondary strata must 

 have been greatly strengthened in this way. We may be sa- 

 tisfied of this, by looking at any great dike of whinstone (such 

 as that of twenty or thirty yards in breadth, now opened on the 

 north side of Edinburgh, as a quarry for pavement), crossing 

 and connecting substances of every variety of hardness; also 

 at the two small dikes which appear crossing the loose shale 

 in the bed of the Water of Leith, close to the two mineral 

 springs. 



The introduction of this new substance, and the heave of 

 the superincumbent mass, which is its necessary consequence, 

 have been productive of several very important results, which 

 shall be the subject of a future communication to this Socie- 

 ty. Let us confine ourselves at present, however, to the con- 

 volutions of the killas. 



According to the Huttonian theory, that loose assem- 

 blage of sand of various qualities, which was destined to give 

 birth to strata of every sort, from gneiss to sandstone, lying 

 originally in a position nearly horizontal, as deposited in beds 

 at the bottom of the sea, and being acted upon from below, 

 on successive occasions, by a heat of great intensity, must be 



conceived, 



