Relations of the Secondary Strata in the Isle of Arran. 23 



the hills above Brodick wood, tlie chain of schistose rocks is wanting, and 

 enormous masses of secondary conglomerate may be traced nearly to the base of 

 the precipices of granite, and probably rest immediately upon that formation. 



Prom lorsa water to the south side of Catacol bay, different varieties of 

 micaceous and chloritic schist occupy the coast ; and, on the whole, appear 

 by their dip to conform to the mineralogical centre. At Catacol bay, two 

 great spurs of granite advance towards the coast, and seem to have cleft 

 asunder the whole chain of slate rocks, which on opposite sides of the bay 

 dip to the N.W. and S.W., — an effect apparently produced by dislocation. 



Prom Catacol bay to the hills which rise on the north-eastern shore of 

 Loch Ranza, the zone we are describing is chiefly composed of a quartzose 

 variety of chloritic slate. The dips are various ; but on the whole the beds 

 incline towards the interior of the island, and appear, therefore, to abut 

 against the granite. 



Prom the mountains which rise to the N.E. of Loch Ranza, the primary 

 slates form a continuous ridge stretching in a south-easterly direction ; but 

 they gradually thin off, and disappear in the upper part of the glen of North- 

 Sannox. In this region the rocks no longer exhibit the same crystalhne 

 texture which they did in the former part of the range; and the dip again 

 begins to conform to the mineralogical centre. • In the slate quarries of GJen 

 Halmidel they resemble some varieties of Cornish Killas ; and in the hill above 

 the salt-pans called Laggan Camp, we in one instance found them passing into 

 a conglomerate form. 



Above Brodick wood the zone of slate reappears, and again takes its place 

 between the secondary formations and the granite, and ranges across the 

 island to lorsa water. Its superficial extent in tiiis part of its range has not 

 yet been well laid down, and its southern limits are perhaps obscured by over- 

 lying masses of trap. In the brow of the hill overhanging the south side of 

 Glen Luig, we found it in a form often put on by the middle zone of the slate 

 rocks of Cumberland, associated with an irregular bed of gray cry.stalline lime- 

 stone, and traversed by a dyke of decomposing trap. 



Prom all these facts, it follows that the slate rocks of Arran have not been 

 successively deposited upon the granite in any regular order, which is indicated 

 either by the mineralogical character, or the superposition of the component 

 beds. Were there any doubt on this subject, it seems to be set at rest by 

 the celebrated junction of Tornignion ; where a whole mountain (composed 

 of strata partaking of that dip to the interior, which was mentioned above,) is 

 seen to abut against the granite, which moulds itself into the broken edges, and 

 in the form of veins is prolonged into the fissures and gaps of the schistose mass. 



