1871.] 



GEIKtE TERTIARY VOLCANIC K0CK3. 



287 



north, end, it slopes gently along the 

 length, of the island to the south end. 

 In the southern half of the island, 

 however, the ground rises, owing to 

 the preservation of an upper mass of 

 beds, which denudation has removed 

 from the northern half of the island. 

 On this rising part of the plateau 

 stands the distinguishing feature of 

 the island, the strange fantastic ridge 

 of the Scur of Eigg. Seen from the 

 north or south, this portion of the 

 island looks like a long steep hill- 

 crest, ending in a sharp precipice on 

 the east. But when we get to the 

 east side, the precipice is seen to be 

 the end of a huge mountain-wall, 

 which rises vertically above the basalt 

 plateau to a height of more than 350 

 feet. It will be seen from the ac- 

 companying map (fig. 1) that this 

 ridge of the Sour corresponds with 

 the area occupied by a mass of pitch- 

 stone, and that while the basaltic 

 rocks cover the whole of the rest of 

 the southern half of the island, they 

 gradually rise towards the north, and 

 successive beds of the oolitic series 

 make their appearance until, at the 

 cliffs of Dunan Thalasgair, the latter 

 cover the greater part of the surface, 

 and leave the volcanic rocks as a 

 mere stripe capping the cliffs. 



In the accompanying section (fig. 2) 

 the general structure of the island is 

 represented. 



B. LlTEEATUEE OV THE StTBJECT. 



Several geologists have published 

 descriptions, more or less detailed, of 

 the mineralogy and geology of this 

 interesting island. In the year 1800 

 Professor Jameson gave a brief ac- 

 count of the different rocks noticed 

 by him in Eigg ; but he did not at- 

 tempt any description of its geological 

 structure, further than to notice that 

 one variety of rock occurred above or 

 below another. He was then fuU 





rg 



s 



o 



I 







!>5 



a 





> QQ 



O <a 





^•fi 





-S -i5 Oi 



o ooo 



(72 rg (jq 



Ml 

 III 



^ !^ <0 

 "o '"' '3 



^•^ 



