20 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 22, 



the Broadford-limestone ; while, as the strata pass towards Suishnish, 

 the Pabba-shales supervene. I know of no other locality where a 

 similar section can be seen. Macculloch indeed describes one on the 

 shores of Loch Eishort near Borereg*. But he has mistaken the 

 quartz-beds there for altered sandstones, and consequently has been 

 deceived as to the true character of the interstratified limestones. 

 They are assuredly not metamorphic, for they contain Ammonites, 

 Gryphcece, and comminuted fragments of shells, and are identical in 

 position and texture with the beds along the Broadford shore f. 



The amount of alteration is not uniform throughout the meta- 

 morphic area. It is greatest in the immediate vicinity of syenite, and 

 slightest where that rock is at a distance. Perhaps the most thorough 

 degree of alteration has taken place in that limestone-patch enclosed 

 in the syenite of Beinn an Dubhaich, whence Lord Macdonald has 

 quarried some large blocks of snowy whiteness. It is exceedingly 

 hard, and probably could not be worked without considerable labour 

 and cost. It has moreover the defect of losing its brilliant purity 

 on exposure : a fragment that was polished about twenty years ago 

 has a dirty yellow surface, while a piece of Carrara marble that was 

 prepared at the same time is still as bright as at first. 



A less amount of metamorphism is discernible among the knolls 

 round Torrin, where the marble possesses in some places an easily 

 discernible stratification, and dips north-west at from 20° to 37°. 

 The texture of the rock at these points is usually crystalline, some- 

 times dull and compact, having a bluish-grey shade that merges on 

 the one hand into white, and on the other into a dark leaden-blue. 

 The faintest trace of alteration can be observed at the spot on Loch 

 Slapin, where the metamorphic shades off into the unaltered rock. 

 In these instances, as in the district generally, the amount of meta- 

 morphism is regulated, on the whole, according to the proximity of 

 the igneous rock. But, as stated above, the alteration in parts of 

 the district removed some way from any syenite is still so great as to 

 suggest that it may have been produced by igneous masses which, 



* Description, vol. i. p. 327. 



f The section given by Macculloch (Description, pi. xiv. fig. 2) of the northern 

 coast-line of Loch Eishort bears at best but a remote resemblance to nature. 

 The long ridges of marble, which he there inserts, have no existence ; and the 

 vast tract of syenite, represented as stretching away eastward across the red sand- 

 stone, is equally imaginary. 



Another section {ibid. pi. xviii. fig. 3), explanatory of the occurrence of the 

 marble, cannot be passed over without comment. It is entitled a " Sketch of the 

 relative position of the marble and shelly limestone at Kilbride." Now it so 

 happens that at Kilbride there is no shelly limestone. The whole district is one of 

 crystalline marble, except at the roots of Beinn Dhearg, where the shales already 

 described occur. Nor is there, that I am aware, either at Kilbride or anywhere 

 else in Strath, such a thing as a mass of marble intercalated with shelly limestone 

 in the way shown in this section. He observes that " these circumstances are 

 all much more obvious in nature than in the sketch." Yet I have very carefully 

 gone over the whole of that locality without discovering where the sketch was 

 taken, or what appearances it was intended to represent. The only passage of 

 marble into shellyjlimestone is that noticed above ; but the repeated intercalation 

 of the one rock with the other, so very obvious in the sketch, is not observable 

 in nature. 



