15$ MR CUNNINGHAM ON THE GEONOSY OF 



we in several places find a rock of a conglomerated cha- 

 racter; angular-shaped masses of pitchstone-porphyry, the 

 same as that of the Scuir, with fragments of trap appear- 

 ing to be imbedded in a base of yellowish or reddish- white 

 earthy claystone. In the already published accounts of 

 Eigg, this rock is described in some instances as a con- 

 glomerate, and in others as a trap-tuffa. Its fragmentary 

 character, however, we view as entirely deceptive, both 

 from the circumstance of its almost passing into the great 

 mass of the Scuir, and from the fact, that the apparently 

 imbedded fragments, when a fresh fracture can be obtained, 

 make a transition into the containing base : in short, we 

 consider it as one of those pseudo-tuffas which we have 

 observed in many other parts of Scotland. Dr MacCul- 

 loch states, that fossilized wood is met with in the rock 

 we have just noticed. This, however, we must dissent from, 

 for, though this wood has never been found in situ, it is 

 evident from the point where its fragments may be ob- 

 tained, that its matrix is the rock of the Scuir ; and this 

 is farther proved, from its always being found in greatest 

 abundance after atmospherical agents have loosed a por- 

 tion of the columnar rock. The internal structure of the 

 wood has been examined by Mr Nicol of Edinburgh.* 



* This minute observer remarks, in the Edinburgh New Philosophi- 

 cal Journal, vol. xvi, p. 154, that " The Eigg fossil in the transverse sec- 

 tion presents annular layers well defined, and displays the coniferous 

 reticulated texture in great perfection throughout the greatest part of 

 the surface. In some few parts, towards the outer edge, the texture 

 is very much distorted, and in one part nearly obliterated. The obli- 

 terated part is replaced by small translucent circular portions of sparry 

 matter, which in some parts are distinct, but in other parts completely 

 confluent. Portions of this small circle of spar casually occur in the 

 perfectly reticulated part, which some have considered as lacunae ; but 

 those towards the outer side not only become larger, but gradually ap- 

 proximate each other, and at last entirely obliterate the meshes. That 

 the whole are not lacunae, may also be inferred from this circumstance, 



namely. 



