MULL. GEOLOGY. 569 



to be fir, which at least it perfectly resembles in its anatomi- 

 cal structure. In its chemical nature it resembles the species 

 of lignite known by the name of Cologne earth, and 

 like that, it forms a most beautiful intense brown paint. 

 The phenomenon of wood in basalt has been often 

 quoted as an argument against the igneous origin 

 of that substance. Whatever conclusions are to be 

 drawn from this fact, it is at least necessary to be 

 accurate in stating it ; and I believe that in all the instances 

 hitherto described, the wood has, as in the present case, 

 been found in a conglomerate or in some other rock, 

 either lying under, or entangled in the basalt, and not 

 in the basalt itself. In none of these cases does it appear 

 to prove any thing either for or against that theory. Wood, 

 it is well known, can be carbonized by the action of water 

 as well as by fire, and as yet no instance of this nature 

 has been brought forward in which the action of either 

 might not equally have produced the effect. If there 

 is a difficulty here peculiarly worthy of remark, it is 

 the circumstance of a vein being thus filled with a 

 conglomerate and containing at the same time a ligneous 

 substance, like this, so little disturbed. It adds one 

 more to the number of conglomerate veins of which 

 I have already described a remarkable instance in Lewis. 

 I must not conclude the examination of the middle 

 district without remarking that this trap extends with 

 little or no variation along the north shore of Loch 

 Scredon, in low terraces, often assuming columnar forms. 

 In one place it entangles a mass of the primary strata, 

 the only instance in which these rocks are found on the 

 northern border of this inlet. 



The southern district, which occupies the whole southern 

 line of shore from the termination of the primary strata 

 to the sound of Mull, and is bounded to the north 

 by Loch Scredon, displays, like those already described, 

 almost every modification of external aspect under which 

 the trap rocks are to be found. Columnar forms occur 



