174 SCARBA. GEOLOGY. 



that section of it which may be seen from Coryvrechan ; 

 which also serves, as will hereafter be found, the addi- 

 tional purpose of explaining the structure both of Jura 

 and Isla. The reader is however already prepared to 

 understand it from the description of Lunga which has 

 preceded. 



The principal body of the mountain is formed of quartz 

 rock, disposed in beds with the same northerly direction 

 as those of Lunga, and like those also, dipping towards the 

 east in angles of forty or fifty degrees. The edges of 

 these beds, as they succeed each other in steps, and their 

 flat surfaces, may be traced every where throughout the 

 island, and they are always very distinct where the natu- 

 ral sections are exposed. In this respect, as well as in 

 the absolute identity of the rocks of which it is formed, 

 Scarba is perfectly similar to Lunga ; and it is equally 

 apparent that these two islands are portions of one 

 continuous ridge of primary strata. As I have already 

 described some of the most remarkable characters of 

 the predominant substance, quartz rock, and shall have 

 occasion, when treating of Jura, to enter again more 

 particularly into the details both of its mineral cha- 

 racters and geological relations, it is unnecessary to 

 dwell on them here. Many varieties occur throughout 

 this extent. There is here also, as in Lunga, to be seen 

 in distinct sequence with the ordinary strata, that rock 

 which although existing in Jura, is there, from the nature 

 of its geographical position, incapable of being examined 

 to the extent requisite for determining its relations to 

 these. This is the fine conglomerate ; composed of 

 quartz, clay slate, and micaceous schist, cemented by a 

 paste of the two latter substances ; beds of it being found 

 alternating with the common quartz rock. It is precisely 

 similar to some of the most frequent varieties of gray- 

 wacke ; but the considerations arising out of this fact 

 must be deferred until the whole series can be examined 

 in one collective view. 



The quartz rock of Scarba, like that of Lunga, is found 



