632 REPORT— 1901. 



Among the older rocks a series of dark schists and cherts has been discovered 

 in North Glen Sannox. They are probably of Arenig age, though no organic 

 remains have been found in them, are closely related to the rocks of Ballantrae in 

 Ayrshire, and similar beds occur in various places along the Highland border 

 where they have been described by Messrs. Barrow and Clough. In the isle of 

 Arran these rocks are intimately connected with the Highland schists. 



The Old Red SancPstone of Arran has been found to comprise two subdivisions, 

 and in North Glen Sannox the upper division is unconformable on the lower. 

 This formation is not confined to the ground north of the String road as generally 

 supposed, but extends in places threa miles to the south of that road, being well 

 developed in the Clachan Glen, where it is much metamorphosed by intrusive 

 igneous rocks. No fossils have been found in the Old Red Sandstone of Arran 

 except rsilophyton jvincejjs, specimens of which have been obtained from the 

 lower division in Glen Shurig. 



The Carboniferous formation, fine sections of which occur on the shore at 

 Corrie and at Laggan, is now known to occupy but a small portion of the area of 

 the island. Near Brodick Castle and in Glen Shurig its width of outcrop is not 

 much more than 200 yards, and it does not reach the western shore, being over- 

 lapped in the interior by unconformable beds of New Red Sandstone. Beds 

 probably of Coal Measure age with characteristic Upper Carboniferous fossils have 

 been recognised at Sliddery Water Head, Corrie, The Cock, and in various other 

 places, but these have no great thickness and contain no seams of coal. They 

 represent apparently the basement beds of the Coal Measures. 



The stratified rocks of the southern part of the island, consisting of red sand- 

 stones, conglomerates, and marls, have been proved to repose unconformably on the 

 Carboniferous formation and in places they contain derived pebbles with Carboni- 

 ferous fossils. All the evidence points to t"heir being of Triassic age, and they may 

 easily be divided into two series, the lower of which probably represents the Bunter 

 sandstone, and the upper the Ke'uper marls. These Triassic rocks occupy the 

 whole of the coast from Corrie southwards, around the south end of the island, and 

 the west coast up to Machrie Bay, where they appear to lie conformably on the 

 Old Red Sandstone. They also form a small area in the north-eastern part of the 

 island near The Cock. 



That still more recent formations once existed in the island, whence they have 

 been removed by denudation, is proved by the presence of fragments of Rhaetic, 

 Liassic, and Cretaceous rocks in a large volcanic vent which is probably of 

 Tertiary age. _ These fragments occur on the western side of the island in the 

 district of Shisken, on the slopes of Ard Bheinn, and they have yielded a con- 

 siderable number of characteristic fossils which have been examined and deter- 

 mined by Mr. E. T. Newton. 



Some of the most important of the discoveries are those connected with the 

 old volcanic rocks of the island. 



A series of interbedded lavas and tuffs is found in North Glen Sannox associated 

 with the schists and cherts previously mentioned. Like them they are probably 

 of Arenig age and closely related to similar rocks at Ballantrae in Ayrshire. 



Two distinct volcanic platforms have been found in the Old Red Sandstone 

 of the island. One set of basic lavas is intercalated in the lower division on the 

 west side of the island, and another occurs in the upper division of North Glen 

 Sannox. 



In addition to the volcanic series previously known in the Lower Carboniferous 

 rocks two others have been discovered in the upper part of the formation. 



That the island was the seat of volcanic activity in times still more recent is 

 proved by the recognition of a large volcanic vent in the Shiskin district, which 

 must be of post-Cretaceous age, as shown by some of the fragments it includes. 



From these facts we conclude that the island has been the scene of volcanic 

 action at no less than seven different periods. 



Mucli has also been learned with regard to the distribution and age of the 

 various intrusive igneous rocks. Two masses of a somewhat intermediate 

 character found in Glen Rosie and in Glen Sannox are probably of Old Red Sand- 



