342 ARRAN. GEOLOGY. 



he may speculate, with the certainty that he has before 

 him a set of incontrovertible data from which to reason. 



BEFORE entering on the details and geological con- 

 nexions of the particular substances which enter into 

 the structure of Arran, it will conduce much to perspi- 

 cuity to give a general topographic sketch of their posi- 

 tions. The perpetual transference of the attention from 

 the geological to the geographical places of the rocks, 

 tends otherwise to produce a confusion both in the de- 

 scription and in the reader's ideas, since these different 

 relations are often very discordant. 



The* greater part of the shores of this island may 

 be considered as formed of red sandstone. This rock 

 is, to an unphilosophical eye, the lowest, and maintains 

 the same apparent position both in the northern and 

 the southern divisions. The geologist alone assigns its 

 true place, and proves that in the former tract it is supe- 

 rior, in the latter inferior, to the more elevated interior 

 rocks by which it is accompanied. This sandstone is 

 tolerably continuous from Brodick to Kildonan castle, 

 where it is obscured or displaced by a body of trap, and it 

 is found to reach to a considerable distance in the interior 

 of the island. It re-appears, covered only with alluvial 

 matter, between Kildonan and Sliddery, where it is again 

 lost, giving way to a range of porphyry that extends 

 as far as Blackwater. Here the strata recur a third time, 

 alternating (topographically speaking) with claystone 

 and porphyry as far as Drumodoon, when they become 

 more continuous, extending to Tormore. At this place, the 

 occurrence of a considerable alluvial tract prevents 

 the fundamental rock from being discovered, but beyond 



* Plate XXII. fig. 3. This section, it must be remarked, is merely 

 intended to convey an abstract idea of the relations, not a picture 

 of the proportions or situations of the rocks. 



