RELATIVE AGE OF THE GRANITES. 27 



The appearances here, in connection with the other relations 

 already noticed, certainly favour the idea of a late intrusion 

 of the fine granite. Some importance, however, must be 

 attached to the occurrence of the rounded pieces of fine- 

 grained granite enclosed in the conglomerate, close to the 

 Craig-Dhu granite (Art. 12). If our explanation of their 

 occurrence there by injection be deemed unsatisfactory, then 

 will not the above conclusion hold; and it must be admitted 

 that, before the irruption of the Craig-Dhu granite, the fine- 

 grained variety of the interior must have been elevated, 

 stript of its slate covering, and exposed to degradation. 



15. What then, it may be asked, is the conclusion which 

 we favour, and to be finally drawn from these various and 

 somewhat conflicting statements? The discussion may seem 

 tedious and unimportant to many; yet we hope it will not 

 be without its use to the student and future inquirer; and 

 as several of the facts are new, it may have some value in 

 the eyes of the many geologists in this and other countries, 

 who have either written upon the subject or take a lively 

 interest in the physical history of this extraordinary island. 

 The question of relative age is, we hope, at least much 

 narrowed by these statements, if it cannot be held as quite 

 settled. 



The various possible conclusions may be set forth, by way 

 of recapitulation, as follows : 



(1). The oldest rock in the island is the slate; it was 

 elevated and exposed to disintegration ere yet the granite 

 had reached the surface, or probably been even intruded 

 among the slate strata. These had, however, been invaded 

 by trap dikes ; for we find at the mill-dam, on the ascent of 

 Goatfell, a basaltic dike intersecting the slate, and itself 

 intersected by a granite vein ! 



(2.) The old red sandstone, and the carboniferous sandstones 

 with their intercalated limestones and coal strata, were 

 formed before the granite was exposed to disintegration, the 

 only fragments of this rock yet found being those in close 



