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massive sandstones. A short distance below the lowest limestone, 

 a dike of felspar rock, or quartziferous porphyry, fifteen to twenty 

 feet wide, crosses the bed of the river, ranging nearly N. and S. 

 The sandstone is greatly altered by it. Between this point and the 

 alluvial plain there are several veins or beds of clay stone and greenstone, 

 breaking through the sandstone of the river bed. In the village of 

 Lamlash we may pay a visit to John Allen, the only collector of mine- 

 rals and fossils that we know of in Arran, and engage his services for 

 an excursion to Ceim-na-Cailliach. 



EXCURSION XI. 



To CEIM-NA-CAILLIACH AND THE CASTLES. 



100. EXCFBSIONS in Arran may be varied indefinitely according to 

 the taste and objects of the tourist or student. We have indicated 

 a few best fitted to show the geological features of the island ; and 

 as we have now described the different formations and the most 

 remarkable appearances which they exhibit, we shall only mention 

 shortly the chief remaining objects of interest which in other excur- 

 sions might be visited. 



The principal object in our present excursion will be to look for 

 " the black crystals," as the smoke-quartz crystals are called. Their 

 chief repository is the north side of the Suithi-Fergus ridge, and 

 that of the Castles. They are found in the coarse-grained and 

 rapidly disintegrating granite of the great northern ridge. Allen 

 knows their localities, and is often successful in collecting them. We 

 pass up by the N.E. angle of Glen Sannox, and then diagonally along 

 the back of the ridge. 



Ceim-na-Cailliach, or the Carlins' Step, is an immense chasm or 

 gash in the ridge, overlooked by granite walls several hundred feet 

 in height. The interior of the fissure can be easily reached by 

 entering laterally at a pretty low level on the north side. We find 

 it to be merely a whin dike worn down to this great depth below 

 the containing granite. The rock is a dark coloured fine-grained 

 greenstone of loose texture ; it exhibits the concentric spheroidal 

 structure so often alluded to as characteristic of common whinstone. 

 There is no trace of any other rock ; and we cannot understand how 

 it has come to be so often said that this dike is pitchstone. The 



