71 



The Outlying Granites. 



49. 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 Article. One of these was dis- 

 covered by Mr. Eamsay in 1837 ; but the first description of it was 

 published in 1839 by M. Neckar, who named the district Plover- 

 field. 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 posi- 

 tion 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. These tracts are represented in the annexed 

 ideal section from east to west between Corriegills and the valley of 

 Mauchrie water, the horizontal extent of the intervening sandstone 

 being much contracted : 



(a) Granite of Ploverfield ; (6) new granite tract at Craig- Dhu; (c) old red sand- 

 stone of Mauchrie water ; (d~) sandstone with beds of limestone, the whole of car- 

 boniferous age; (e) eruptive rocks of Doir-nan-Each, the highest hill in the west district 

 cfthe south section of the island, chiefly porphyry and highly hornblendic basalts. 



The Ploverfield Granite. 



50. The Ploverfield granite occurs amid strata which undoubtedly 

 belong to the carboniferous system. The tract is situated on the 

 west side of Glen Cloy, and that branch of it called Glen Dhu. The 

 hills here are the highest portion of a long ridge running up south- 

 west from the plain of Brodick, and dividing Glen Cloy from Glen 

 Shirag. At the origin of this ridge, are beds of carboniferous lime- 

 stone with fossils, under the north wall of the enclosure of Brodick 

 church. On the upper slope of the ridge, beds of limestone and 

 shale also occur in the sandstone, not far from the north base of the 

 Windmill hill a high, elongated, narrow ridge, steeply overhanging 



