690 VEINSTONES. 



pointed out in the author's work on the Western 

 Islands, veins of an entirely different nature have 

 been observed, consisting of rounded fragments of 

 different substances, compacted into a solid conglo- 

 merate, and resembling many of those which 

 were described in the last article. Where one of 

 the including walls of such a vein has fallen away, 

 it presents the unexpected appearance of a bed or 

 stratum of conglomerate, at angles to the strata in 

 which it lies. It is important to point out this 

 variety ; as it might otherwise mislead a geologist, 

 so as to give rise to erroneous conclusions. It is 

 evident that it must have arisen from the consoli- 

 dation of loose materials which have casually 

 fallen into open fissures. 



It is lastly interesting to remark, that the con- 

 i@nierate veins which are occasionally found 

 among the rocks of the trap family, and which are 

 formed of their fragments, sometimes contain or- 

 ganic substances, namely, portions of bituminized 

 wood, or of lignite. A very remarkable instance 

 of this nature occurs in Mull, where a large portion 

 of a tree is thus situated. Erroneous conclusions 

 respecting the oiugin of the trap family, have thus 



