568 MULL. GEOLOGY. 



great regularity and beauty ; constituting specimens of 

 convenient dimensions for collectors of minerals. 



Of the amygdaloids found here I may notice two 

 varieties, as being uncommon. One of these is a soft 

 grey rock of a texture resembling indurated clay, con- 

 taining nodules of chlorite of different sizes, hollow and 

 crystallized within ; similar to those occurring in the hill 

 of Kirinoul, but more perfect and more numerous. The 

 other contains quartz nodules, together with rounded no- 

 dules of heliotrope, of a dark green colour, but without that 

 variety of aspect which is to be found in them in Rum. 



The last substance which it is necessary to notice 

 as occurring in this trap, is carbonized wood. I shall 

 particularize only one of the spots where it is found, 

 because I am enabled to give a sketch that will render 

 it intelligible.* There are others, but not of such easy 

 access. This substance is contained in a perpendicular 

 vein, about fifty feet in height, and five feet in breadth, 

 the lower end of which reaches to the shore ;f the 

 upper terminating abruptly in the mixture of solid and 

 columnar basalt by which it is every where surrounded. 

 The upper part of this vein is a conglomerate of soft 

 grey trap fragments imbedded in a paste of the same 

 materials. Toward the bottom it varies and becomes 

 mixed with a black substance, which on examination 

 is found to consist of minute fragments and a fine 

 powder of carbonized wood, the vegetable organiza- 

 tion being still visible in the former. Amongst this 

 black matter a portion of the trunk of a tree appears, 

 in a direction parallel to the side of the vein, and therefore 

 erect, being entire and unbroken for the space of at 

 least s^x feet. It is traversed by a vein of crystallized 

 lime spar. On careful examination of this wood it appears 



* Plate XXI. fig. 1. 



f These proportions are neglected in the sketch for the convenience 

 of giving the more interesting part of a sufficient size. 



