of Ihc Island of Bute, 



85 



III. The Lignite Beds. 



7. The trap rocks a(; Ascog derive their chief interest from 

 being the repository of beds of lignite; a substance so rare in 

 Scotland, that I believe no well-marked beds occur on the 

 mainland, and but few in the other islands; and these in 

 situations very difficult of access. I was led to a careful ex- 

 amination of this carbonaceous deposit by the statement of 

 Dr. MacCulloch, that some of the beds occurring here were 

 unlike any he had seen in his survey of the western islands. 



The principal bed is situated in the face of the cliffs above 

 the road, a little to the south of Ascog Mill, as shown in the 

 annexed section giving the various beds. 



s, sandstone ; r, terrace and road ; ff, greenstone ; a, trap-tuff; b, red 

 ochre; c, lignite bed; d, pisolitic ochre; e, porphyritic amygdaloid, the 

 upper portion much-altered. 



The lowest bed resting on the sandstone is a small-grained 

 rudely columnar greenstone; the junction is, however, con- 

 cealed. Over this is a trap-tufF with a base of greenstone, 

 and imbedded spherical lumps of the same substance. This 

 is followed by a bed of red ochre of coarse texture, traversed 

 by numerous black iron seams, which have doubtless been 

 produced from a change in the oxidation of the component 

 iron. Over this is the lignite bed : it is three feet thick, and 

 consists of hard stony coal, interstratified with a yellowish- 

 white shale, both being much intermixed with pyrites. The 

 coal has been so much altered throughout its whole thickness 

 by the contact of the trap rock, that Mr. Rose of Edinburgh, 

 to whose examination I submitted the best specimens I could 

 find, in order that he might determine the species of wood, but 

 without mentioning the geological situation of the coal, was 

 "unable to obtain a slice in consequence of the structure being 

 altered by the contact of a whin dike." The coal has been 



