



ISLE OF MAN. GEOLOGY. TRAP VEINS. 571 



which are found accumulated in beds in almost every part 

 of the island. It is not difficult to imagine that such 

 substances were deposited during the progress, or after 

 the termination of the calcareous formation, and that they 

 were distributed over the surface of the beds and indurated 

 into their present condition, before the sea had quitted 

 the rocks, or these had emerged from the waters. 



I must now proceed to the last of the rocks, namely, 

 the trap veins ; the particular description of which was 

 reserved to this place, to avoid interrupting the more 

 interesting parts of their general history. 



The places of those which were observed, have already 

 been pointed out in speaking of the limestone. The 

 general connexion of these with the stratified rock, and 

 the influence, apparent or real, which they may have pos- 

 sessed over its character and disposition, have already 

 been sufficiently described. It only remains to notice the 

 individual specimens in greater detail than could then have 

 been conveniently adopted. 



Some of the smaller, which occur near Scarlet point and 

 at Pool vash, are composed of an ordinary fine greenstone, 

 which in certain places becoming perfectly compact, 

 smooth, and uniform, may perhaps be considered as a 

 basalt. These basaltic specimens are, in general, of a dark 

 lead blue, but I observed one vein not exceeding an inch 

 in breadth, of a glossy black, nearly resembling in lustre 

 and compactness the basis of the well-known porphyry of 

 Egg. It traverses a smooth conchoidal limestone, with 

 which it is firmly united at the edges. 



The principal veins near Scarlet point present a porphy- 

 ritic texture. The basis is here of a pale or dark grey, 

 and the crystals of felspar are of the same colour, being 

 very conspicuous, and possessing the common as well as 

 the glassy lustre. In some places these veins are decom- 

 posed ; or rather, they have undergone the change which 

 precedes decomposition, to such a depth, as to put on the 

 deceptive appearance of a common yellow felspar por- 



