["HE ISLE OF EIGG. | ;">:-} 



places, small vesicular cavities in the felspar, and as to 

 such the pitchstone owes its colour, the formation of both 

 must have been of the same general description.* 



The only other pitchstone which was formerly known 

 to exist in Eigg is that which, from the name of its eastern 

 extremity, may be styled the range of the Scuir. It forms 

 a lofty and, to the south, precipitous wall, which crosses, 

 with little interruption, the southern part of the island, 

 presenting an outline of a very striking character, and 

 totally different from the mountainous and wild eminences 

 of the highlands of Rume and Skye. In regard to the 

 relations of the pitchstone-porphyry of the Scuir and the 

 trap-rocks with which it is connected, it can, after a most 

 careful examination around the whole mass, be confidently 

 asserted, that it exists as a great vein which has been 

 erupted through the older Plutonic rocks, thus agreeing 

 in age with all the other pitchstones of the island. At 

 the eastern extremity of the Scuir, its posteriority to the 

 trap is most distinctly visible, inasmuch as it cuts through 

 perfectly horizontal beds of basalt and amygdaloid which 



* So early as the year 1808, Professor Jameson, in his Mineralogy 

 of the Scottish Isles, vol. i. p. 48, says, when describing the Arran 

 pitchstones, " When pounded it emits a bituminous smell, which ren- 

 ders it probable that it may contain inflammable matter." Chemical 

 analysis has since verified this conjecture. The pitchstone of Newry, 

 in Ireland, described in the Transactions of the Royal Society, was 

 found by the Hon. G. Knox to contain the following components : — 

 Silica, 78.800 ; alumina, 11.500; lime, 1.12; protoxide of iron, 3.036; 

 soda, 2.857; water and bitumen, 8.500 ; = 99.813.— EW. Phil. Jour. 

 vol. viii. p. 190. The pitchstone of Planitz, in Saxony, contains bitu- 

 minous matter, and, according to some chemists, the pitchstone of Pots- 

 chappel, in Saxony, contains, besides the usual ingredients, three 

 parts of Lithion. — lb. p. 190. 



In the Lothians, and other i>arts of Scotland, we have found some 

 trap-rocks to be highly charged with bituminous matter. May not this 

 be, in some way or other, connected with the chemical composition of 

 the sedimentary strata through which they have been protruded >. 



