44 



lost in marshy ground for a short distance, but is again continued 

 towards the mountains. In the other direction, its course was satis- 

 factorily made out as far as Portincaple Ferry, where it is well seen ; 

 and a dike of the same width and bearing, which seems to be a pro- 

 longation of this dike, was met with near the top of the mountain on 

 the east side of Loch Eck, traversing mica slate and altering it con- 

 siderably. The width is about twenty-five yards, and it bears a point 

 S. of W. It is in many places inclined at the same angle as the 

 slate, among the beds of which it seems to have insinuated itself 

 in a serpentine course. The mica slate in some places is slightly 

 changed by the contact, being rendered harder and more massive : 

 the lamination is partially destroyed, and the rock is banded, 

 parallel to the sides of the dike. In one place pieces of the slate 

 are seen enclosed in the dike, and slightly altered. Portions of 

 the wedge-shaped mass of slate (d), between the two veins, are 

 entangled in the basaltic dike, and altered in the same manner. 

 The circumstances of this case clearly show the posterior origin of 

 the basalt. 



At the edges the dike consists of blue slaty basalt, but the greater 

 part of the mass is a coarse grained greenstone, which at several 

 points exhibits in great perfection that peculiar structural arrange- 

 ment in concretionary spheroids, which is the most frequent and 

 characteristic form assumed by the trap rocks, and of which the 

 columnar is but the result, when under favourable conditions, they 

 parted more slowly with their heat of fluidity. The best marked of 

 these is in a cliff about sixty feet high, overhanging the marshy 

 ground above mentioned, where the dike has a considerable underlie, 

 the slate being in contact on both sides. It is here divided into 

 columns of spheroids perpendicular 'to the sides of the dike, and 

 separated from one another by imperfect joints. Sometimes each 

 joint is composed of a single spheroid ; one was noticed measuring 

 fifteen inches by ten ; in other cases numerous small closely packed 

 spheroids make up a joint. Instead of a distinct separation as in 

 basaltic pillars, the columns are connected by narrow seams of de- 

 composed greenstone. The columnar structure is here seen in the 

 act of development. If the heat had parted more gradually, a fagade 

 of pillars would have been the result. This spot affords an excellent 

 illustration of the remarkable experiments of Mr. Gregory Watt on 

 fused basalt (Phil Trans., 1804). 



It will appear from the foregoing statements, that the small area 

 we have been describing, is one of considerable interest, exhibiting, 

 as it does, the rare association of many species of erupted rocks in 



