284 Dr. Mac Culloch on the Geology of Glen Tilt. 



white marble which I found in Glen Fernat, not far from the 

 junction of the Brerachan with the Airdle. The well known 

 ancient green marbles owe tliat colour to the same admixture, 

 which indeed in the Egyptian green and the Verde antico, is such 

 that the calcareous matter is overpowered by the serpentine. The 

 aspect of the green marble of Glen Tilt is however perfectly differ- 

 ent from that of any marbles ancient or modern which have yet been 

 wrought, and it offers therefore a valuable addition to the arts as 

 well as a nev/ commodity to the list of our mineral productions. 

 I may add that, with a similarity of composition, many specimens 

 bear a considerable resemblance both in character and colour to 

 some varieties of the Cipolino of the Italians. Two other distinct 

 varieties of marble occur where the calcareous beds terminate. The 

 one is of an uniform ochre yellow, but of a much paler tint than 

 the giallo antico ; the other is of a flesh colour graduating into dark 

 blue, but neither of these beds is of great magnitude. 



The extent of the limestone which I have now been describing is 

 considerable. The mass is of great thickness, and from the obliquity 

 of its section a very large horizontal surface is exposed. As the 

 beds run towards the north they may be traced to a considerable 

 distance up the hill on the right of the river, but dipping to the 

 south they plunge into the opposite hill and disappear. Indepen- 

 dently of the steatitical matter which is mixed with this rock, some 

 interesting minerals are found imbedded in it. The beds where 

 they come in contact with micaceous schistus contain so much mica 

 that this latter becomes at length the predominant substance, and 

 there is then a perfect transition from micaceous schist to marble. 

 In these cases it is raised in thin flags of great extent ; between 

 these flags there are often seen beds of steatitical clay, of a pure 

 white or greenish hue, and often of considerable thickness. In the 



