ARRAN. GEOLOGY. GRANITE. 351 



is universally true, but it is highly probable, as they have 

 frequently been observed to terminate in the granite, and 

 never as yet to pass beyond it ; a circumstance in which 

 they resemble the veins occurring in other rocks, com- 

 monly, if not always properly, called contemporaneous. 

 Among other places, they occur in Goatfell. They are 

 characterized by the smallness of their grain compared 

 to that of the surrounding rock, as well as by a frequent 

 want of distinctness in the constituent parts ; while their 

 sides are often amalgamated with the including substance. 

 Akin to these veins, there occur distinct concretions of 

 similar fine grained granite imbedded in the ordinary 

 kind, and equally resembling the veins, in the intermixture 

 of character which takes place at the points where they 

 join the including mass. This however is an appearance 

 by no means uncommon in granite, and it is particularly 

 frequent in that which extends from Glenco to Rannoch ; 

 where, as in other places, it seems to form but one modi- 

 fication of that very frequent change of crystallization, as 

 well as of aspect, and proportion of ingredients, which is so 

 frequent in this rock. The cause of its concretionary 

 form must for the present remain unknown to us, but 

 such concretions are not peculiar to this substance. They 

 occur in the rocks of the trap family; and Arran itself 

 produces some striking examples of this nature. Another 

 view may be taken of the origin of these concretions 

 in granite, as well as in trap. They may be supposed 

 analogous to the imbedded fragments in conglomerate 

 rocks ; and thus a large grained granite containing masses 

 of a smaller grained variety, may be esteemed a granitic 

 conglomerate; a substance not more unlikely to occur 

 than that, of which the examples seem sufficiently un- 

 equivocal, namely, a conglomerate in which a paste of 

 granite contains fragments of micaceous schist.* 



* I pointed out long ago in the Transactions of the Geological Society, 

 the magnetic property of the granite of Goatfell, and have since confirmed 

 the frequency of this phenomenon from observations made on Cruachan, 



