698 CARBONIFEROUS VOLCANIC ROCKS. [Ch. XXXII. 



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

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

 Ochils, and extending from Stirling to near St. Andrew's. They con- 

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

 earthy and amygdaloidal. They are regularly interstratified with 

 the sandstone, shale, and ironstone of the lower Coal-measures, and, 

 on the East Lomond, with Mountain Limestone. 



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

 drew's, 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. Andrew's, the encroachment of the sea on the cliffs has isolated 

 several masses of trap, one of which (fig. 731) is aptly called the 

 " rock and spindle," * for it consists of a pinnacle 

 rig. TS2. 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 terminations of the columns are seen 

 round the circumference (or tire, as it were, of the 

 ?one m Sen° f eSSse wlieel )> as in the accompanying figure. I conceive 

 at 5, fig. T3i. , this mass to be the extremity of a string or vein of 

 greenstone, which, penetrated the tuff. « The prisms 

 point in every direction, because they were surrounded on all sides 

 by cooling surfaces, to which they always arrange themselves at right 

 angles, as before explained (p. 617). 



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 

 gray sandstone and shale, forming the lowest part of the Old Red 

 Sandstone, but which may probably be of carboniferous date. It 

 may be traced for many miles, passing through the amygdaloidal 

 and other traps of the hill called Norman's 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, perhaps titaniferous, is also present. The 

 result of this analysis is interesting, because both the ancient and 

 modern lavas of Etna consist in like manner of augite, Labradorite, 

 and titaniferous iron. 



Trap of the Old Red Sandstone Period.— Bj referring to the sec- ' 



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

 term for a distaff. 



