16 GEOLOGY OF ARRAN. 



a distant source being thus indicated; while the other is 

 often angular or slightly rounded. It is remarkable that frag- 

 ments of granite do not occur in the conglomerate ; none of 

 the Arran sandstones have as yet yielded a piece of this rock, 

 except in a single instance, where its presence may be other- 

 wise explained (see Art. 12). The conclusion to be drawn 

 manifestly is that when these sandstones and conglomerates 

 were in process of formation by the wearing down of the 

 slate rocks and the transport of the fragments by water, the 

 granite of the interior was not exposed to disintegrating 

 causes, but remained as yet in hypogene depths, protected 

 most probably by the enveloping slate rocks. Facts to be 

 stated farther on will throw light on this curious subject. 



The, Outlying Granites. 



10. Perhaps the most remarkable feature in the geology 

 of Arran is one made known by its recent explorers, and 

 of which the British Isles offer, we believe, only one other 

 example. We refer to two outbursts of granite amid the 

 sandstones of the southern division of the island, noticed in 

 the last three Articles. One of these was discovered by Mr. 

 Ramsay in 1837; but the first description of it was pub- 

 lished in 1839 by M. Necker, who named the district 

 Ploverfield. The other was discovered by the writer of 

 these notices in the summer of 1855, and described in the 

 autumn of that year at the Glasgow meeting of the British 

 Association. Both tracts occur on that side of the sandstone 

 district which is nearest to the " granite nucleus ;" and the 

 occurrence of the rock here is thus intimately related to the 

 outburst of the central granite, in its abnormal position 

 close to the outer border of the upper slate, and to the base 

 of the sandstone formations already pointed out as the 

 great leading peculiarity of Arran. The relation of these 

 granites to that of the nucleus, and to the adjoining strata, 

 is shewn in the annexed ideal section from N. to S. across 

 the granite nucleus (fig. 6) : 



