1ONA. GEOLOGY. 17 



colour it is sometimes of a pure white, but more com- 

 monly it is mottled, or stained with various shades of 

 grey and brown : occasionally also it is of a greenish 

 colour. 



Nearly similar in direction, and removed at a very 

 small distance by a few beds of argillaceous schist, is 

 found the well known marble for which lona has been 

 long celebrated. I should rather say, the place of the 

 marble, as nearly the whole of the bed has been long 

 since removed. Portions of the walls, and those pails 

 which were inaccessible to the quarry-men by reason of 

 the sea, still remain to show what it has been. It is 

 not a regular bed, since it terminates abruptly at a short 

 distance from the sea, but is rather one of those isolated 

 masses which are of frequent occurrence in many of the 

 schistose rocks, as well as in gneiss. It is from twenty 

 to thirty feet in breadth, and is elevated at an angle of 

 80 or 85 degrees, dipping to the eastward and directed 

 towards the south, not above 100 yards of its length being- 

 visible. All the useful parts have been wrought out, 

 and, it is said, but without sufficient foundation, that 

 the high altar of the cathedral consisted of it. That 

 altar has disappeared, whether in consequence of the 

 superstitious avidity of pilgrims and visitors for its frag- 

 ments, as report says, cannot now be determined. The 

 texture of this marble is compact, its fracture splintery, 

 and its colour white, often however with a slight greenish 

 tinge. It is incapable of receiving a polish, its aspect 

 remaining either uniformly dull, or as if mottled with 



ally occurring in the long bladed prismatic hammer. From the sphericity 

 of the surface, that momentum is also directed on one point, instead 

 of being divided over a large space, as in the flat faced hammer, thus 

 producing that vibration by which rocks are split. The relative 

 position of the centre of gravity and the point of -impulse, also 

 prevents that injury to the wrist which so often follows a misdirected 

 blow with the long hammer ; its lever acting against the operator. To 

 these advantages I may add, durability ; the form preventing the steel 

 from flying off, as in the common construction. 

 VOL. I. C 



