S8 GEOLOGY OF THE CAMPSIE HILLS. 



western faces of the hills, it frequently shews this 

 thickness in sections of from 70 to 100 feet, 

 perfectly perpendicular to the horizon. These 

 faces almost always display an arrangement of 

 polygonal columnar forms, which generally rest 

 upon sandstone : But, in some instances, I have 

 observed this great body of trap divided into two 

 beds of nearly equal thickness, the upper bed shew- 

 ing distinctly its strong tendency towards taking co- 

 lumnar form ; but the under bed, upon which these 

 columns stand, being perfectly amorphous, and 

 shewing no tendency to any form whatever. The 

 columnar forms of the trap in the upper bed, al- 

 though clearly apparent, are very irregular in 

 their constructions, as to size, sides, and angles *, 

 no symmetrical similitude is to be observed among 

 them. They have in general from three to six 

 sides, and are of various diameters, from one to 

 seven feet. Their heights, at Murray's Hall, may 

 be traced, in the front of the precipice, from seven- 

 ty to eighty feet, and their positions are in gene- 

 ral vertical. Some of these columns appear to be 

 jointed, but these apparent joints have no regu- 

 larity in position or direction ; and these appear- 

 ances seem only produced by accidental cracks 

 which cross some of the columns. The amor- 

 phous part of the trap, which sometimes is inter- 

 posed between the columnar trap and the sand- 

 stone, is of the same composition as the upper bed, 

 but their component parts differ in their propor- 

 tional quantities j that is to say, that the under 



