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seminated in veins and bands, the rock is capable of taking a fine 

 polish, and of being applied to ornamental purposes ; the colour is 

 dark gray. Between the limestone and the sandstone above it, 

 there is interposed a bed of loose materials, consisting of red sand, 

 marked with round gray spots, and enclosing pieces of limestone and 

 sandstone. Hence the bed of lime must have been exposed to 

 considerable decomposition before the sandstone was deposited over 

 it. A lengthened and careful search was not rewarded by the dis- 

 covery of any fossils. It is, however, obviously in the position of the 

 cornstones of England, 



Several beds separated by strata of sandstone occur on the shore 

 at the mouth of the river. The whole series is here traversed by 

 dikes of greenstone, the largest of which is about sixty feet wide, 

 and ranges about N.N.W.; the others are so numerous, and so 

 ramified, as almost to defy description. They pierce through the 

 limestone in every direction, thin veins branching from the greater, 

 and often again uniting, while small portions of the limestone and 

 sandstone are entangled in the trap, and traverse it in disconnected 

 veins. The changes produced upon the limestone are of the most 

 interesting kind ; we know of no locality in the West of Scotland 

 where the posterior origin and intrusive character of the trap rocks 

 are so clearly manifested, and would strongly recommend it as a 

 point to be visited by the student of geology. The changes which 

 the limestone has undergone run through every variety of external 

 aspect, from the impure, dark coloured, perfectly opaque state, to 

 that of a pure white marble, translucent on the edges, homogeneous 

 throughout, and devoid of stratification, or visible lines of cleavage. 

 Intermediate between these extremes there are an indurated semi- 

 crystalline limestone, a granular saccharine marble crumbling into 

 fine powder under slight pressure, and phosphorescing when thrown 

 upon a heated surface ; a very hard white or blue crystalline marble, 

 having the crystals in distinct plates ; the degree of alteration 

 depending on the distance from the sides of the dike. The 

 entangled portions are among those which exhibit the greatest 

 amount of change. The most altered parts of the sandstone re- 

 semble quartz rock. 



In order to determine whether any and what chemical changes 

 had been induced simultaneously with these alterations of mineral 

 character, and to afford terms of comparison with metamorphic 

 action upon other limestones, Dr. Robert Dundas Thomson most 

 kindly furnished us with analyses of several specimens, made under 

 his own care. These are as follows : 



