532 SKY. GEOLOGY. SECONDARY STRATA. 



ceous schist. With respect to chemical composition it is 

 generally pure ; but where in contact with the syenite or the 

 trap veins, becomes overloaded, not only with silica, but 

 with magnesia and argil also. In such situations it often 

 contains veins and nodules of greenish transparent serpen- 

 tine, and adopts a variety of colours; circumstances in 

 which it also resembles exactly those limestones which 

 in Glen Tilt are found in contact with granite, or at Bala- 

 hulish and in Tirey and lona, with micaceous schist 

 and gneiss. The predominant colour is grey, varying 

 from nearly white through all shades of dove colour to 

 a dark blue grey ; sometimes beautifully striped, and 

 occasionally mottled or veined : in many situations it 

 is of a pure snow white, forming a perfect variety of 

 statuary marble, and affording as yet perhaps a solitary 

 instance of this variety of limestone occurring among 

 secondary strata. In calling this a solitary instance, I 

 may however suggest, that when more attention shall 

 have been paid to geological investigations many of the 

 facts here enumerated will not appear so extraordinary 

 as they now seem. 



It is impossible to conclude this part of the description 

 without inquiring into the probable causes of this con- 

 fusion of character or change of structure in the limestone 

 deposit. It will be easily conjectured that I am inclined 

 to attribute the whole to the influence of the syenite. 

 This rock is found at one place, if not actually in contact 

 with the limestone, at least at a very small distance, since 

 the interval formerly mentioned at Kilbride amounts only 

 to a few feet : in other cases there is a nearer approxi- 

 mation, but, as already remarked, the interior country 

 is too much obscured by soil to admit of very accurate 

 examination. In some places, it is true, the unstratified 

 limestone is found without the syenite, but the absence 

 of this rock is by no means conclusive against its in- 

 fluence. The interior country bears evident and strong 

 marks of recent waste, and the syenite of Sky is every 



