228 Dr. Mac C u l l o c h on the Hill of Klnnoul 



which are supposed by many persons to demonstrate the igneous 

 origin of trap. 



About the middle of the broken face of the hill a portion of a 

 stratum of sandstone is to be observed entangled in the mass of the 

 rock, and at the same time much broken and bent. But there is 

 nothing in its appearance so very different from the other instances 

 of this fact which have been frequently described, as to call for a 

 particular detail. 



Proceeding from this point eastward another set of junctions is 

 seen, of which I have not met with any resemblance in other 

 places, and which offers some anomalous appearances. The strati- 

 fied rock which is here conjoined with the trap, is perfectly similar 

 to the best characterized graywacke slate, of a fine grain and 

 greenish hue. It is easily separated into flakes, and on being 

 broken, exhibits slender scales of mica. A remarkable change of 

 its aspect may be seen where it approaches the trap, and before it 

 comes into actual contact with it. If the weathered surface only 

 be examined, it shews a series of solid laminae alternating with, or 

 rather graduating into other laminae which have a spongy appear- 

 ance, or abound with open cavities similar to those of weathered 

 amygdaloids. These cavities increase in number and magnitude 

 towards the middle of the spongy laminae. The same appearance 

 of pores or cavities is to be observed at most of the points of contact 

 where the graywacke is much contorted and mixed with the trap. 

 A good illustration of this appearance may be given by comparing 

 it with that assumed by the burnt micaceous schist sometimes 

 found in the walls of the vitrified forts, and which by the action 

 of the fire on some of its laminae is swelled up and thickened, 

 apparently from the disengagement of aeriform matter. When, 

 however, this stone is broken, the cavities are found to be filled by 



