Mi{. Bktce on the Geological Structure of Roseneath. 126 



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, besides other gradations, similar to those 

 described in the paper on Bute already referred to, 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 resemble quartz rock. 



15. In order to determine whether any and what chemical changes 

 had been induced simultaneously with these alterations of mineral char- 

 acter, and to afford terms of comparison with the metamorphic action 

 upon limestones of the same age in Bute, (Art. 1,) Dr. Robert 

 Dundas Thomson has most kindly furnished me with analyses of several 

 specimens, made under his care in the laboratory of the University. 

 These are as follows : — 



Specimen No. 1, is the unaltered limestone, as pure a specimen to the 

 eye as could be selected. 



No. 2, is the saccharine marble, crumbling readily into powder, in the 

 same state as No. 1 of the Bute specimens. (Proc. Phil. Soc. Glas. vol. 

 III. page 20). 



No. 3, is the most altered specimen in this locality, described above as 

 " a pure white marble, translucent on the edges," &c., and which turns 

 out to be Table spar. 



No. 4, is a carefully picked specimen of the same, free from carbonate 

 of lime. 



No. 5, is a calcareous sandstone, altered by contact, scarcely distin- 

 guishable from No. 2. 



No. I. 



By Mr. P. Katcr. 



Carbonic Acid, 42*40 



Lime, 54*58 



Silica, 0-70 



Magnesia, 0*40 



Water and loss, 192 



100-00 

 Non. 



Carbonic Acid, 42-52 



Lime, 54-68 



Insoluble Siliceous Matter, 1*14 



Magnesia, a trace. 



98-34 



