Ch. XXXH.] CARBONIFEROUS PERIOD. 557 



wacke, and tuff. They appear to have been erupted while the sediment- 

 ary strata were in a horizontal position, and to have suffered the same 

 dislocations which those strata have subsequently undergone. In the 

 volcanic tuffs of this age are found not only fragments of limestone, 

 shale, flinty slate, and sandstone, but also pieces of coal. 



The other or older class of carboniferous traps are traced along the 

 south margin of Stratheden, and constitute a ridge parallel with the 

 Ockils, and extending from Stirling to near St. Andrews. They consist 

 almost exclusively of greenstone, becoming, in a few instances, earthy 

 and amygdaloidal. They are regularly inters tratified with the sandstone, 

 shale, and ironstone of the lower Coal-measures, and, on the East Lo- 

 mond, with Mountain Limestone. 



I examined these trap rocks in 1838, in the cliffs south of St. An- 

 drews, where they consist in great part, of stratified tuffs, which are 

 curved, vertical, and contorted, like the associated coal-measures. In 

 the tuff I found fragments of carboniferous shale and limestone, and 

 intersecting veins of greenstone. At one spot, about two miles from 

 St. Andrews, the encroachment of the sea on the cliffs has isolated 

 several masses of traps, one of which (fig. 679) is aptly called the 

 "rock and spindle/'* for it consists of a pinnacle of tuff, which may 

 be compared to a distaff, and near the base is a mass of columnar 

 greenstone, in which the pillars radiate from a centre, and appear at 

 a distance like the spokes of a wheel. The largest diameter of this 

 wheel is about twelve feet, and the polygonal termina- 

 tions of the columns are seen round the circumference 

 (or tire, as it were, of the wheel), as in the accompany- 

 ing figure. I conceive this mass to be the extremity of 

 a string or vein of greenstone, which penetrated the 

 tuff. The prisms point in eveiy direction, because they 

 were surrounded on all sides by cooling surfaces, to 

 which they always arrange themselves at right angles, Columns of green 



J . J ° ° ° stone, seen end- 



as before explained (p. 484). wise at &, fig. 679. 



A trap dike was pointed out to me by Dr. Fleming, in the parish of 

 Flisk, in the northern part of Fifeshire, which cuts through the grey 

 sandstone and shale, forming the lowest part of the Old Red Sandstone. 

 It may be traced for many miles, passing through the amygdaloidal and 

 other traps of the hill called Normans Law. In its course it affords a 

 good exemplification of the passage from the trappean into the plutonic, 

 or highly crystalline texture. Professor Gustavus Rose, to whom I 

 submitted specimens of this dike, finds the rock, which he calls dolerite, 

 to consist of greenish black augite and Labrador felspar, the latter being 

 the most abundant ingredient. A small quantity of magnetic iron, per- 

 haps titaniferous, is also present. The result of this analysis is interest- 

 ing, because both the ancient and modern lavas of Etna consist in like 

 manner of augite, Labradorite, and titaniferous iron. 



* " The rock," as English readers of Burns' poems may remember, is a Scotch 

 term for distaff. 



