204 M k. Bryce on the Geology of the Idand of Bute. 



A little above the road, a small-grained, rudely columnar greenstone 

 rests upon the sandstone, but the exact junction is concealed. To 

 this succeeds an ironshot concretionary greenstone, or species of trap- 

 tuft', the base being greenstone, and the imbedded portions being 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 been 

 produced, no doubt, from a change in the oxidation of the component 

 iron. Over this is the lignite bed. It is three feet thick, and consists 

 of a 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 con- 

 tact of a whin dike." The coal has been worked to some extent by 

 driving an adit inwards on the line of the dip, which is about 20° to the 

 westward ; but the workings have been for some time abandoned, and 

 the inner and lower portions are now full of water. It is said that they 

 would be most likely soon resumed, if too high a rent was not demanded. 

 Beds, indeed, so situated, and of such a character, can never bo expected 

 to yield much profit, or to be of any considerable economical advantage. 



The floor of the coal has been already described : the roof, d, is a 

 peculiar rock. In consists of a base or paste of an ochreous steatite, with 

 imbedded round pieces of the same substance, and may hence be called a 

 pisolitic ochre ; it is 3} yards thick. The bed above this is of the same 

 character, but the base contains less soapstone, and with the imbedded 

 steatite it contains also imbedded calcareous spar. The base effervesces 

 briskly with an acid ; and hence we may call the rock a calcareous 

 amygdaloid. The upper portion of this bed, to the thickness of a few 

 inches only, is very hard, and has a semivitreous appearance, and thus 

 closely resembles a porphyry. In common with the trap above — and, 

 indeed, all the beds in this locality — it contains much disseminated iron. 

 The rest of the cliff is occupied by greenstone, which is the same as the 

 lower bed resting on the sandstone. 



Another bed of lignite occurs on the opposite, or north-west side of the 

 trap district, overlooking Ascog lake. The coal dips to the interior 

 of the area, that is, nearly south. It is of about the same thickness, and 

 is accompanied by beds of steatite and red ochre very similar to those 

 above described ; but the nature of the ground is such that a complete 

 section cannot be had, and the precise number, therefore, and order of 

 the beds cannot be exactly stated. The association, however, of the 

 lignite with ochres and steatites here also is sufficiently distinct, and it is 

 even probable that these beds are persistent throughout the whole of 

 this district. It is to these ochreous and steatitic beds that Dr. MacCul- 

 loch refers, when he says, that he " has met with no similar substance 



