oO GEOLOGY OF ARRAN. 



These are all intimately connected, one species often 

 passing into another by regular gradations, and they are all 

 found in the same relative positions with respect to the 

 sedimentary strata. Among themselves they do not preserve 

 any order of succession, nor do they occupy separate areas, 

 so that their continuity cannot be reckoned on through a 

 considerable space. Nor can they be indicated on a map by 

 distinct coloui's, so intimately are they blended with one 

 another. Basalt, diorite, amygdaloid, and porphyry are by far 

 the most abundant, as well in overlying masses as in dikes 

 and interposed beds. Porphyry is next in abundance, and 

 occurs in all these positions; pitchstone alone has not over- 

 flowed the surface, and occurs only in dikes and beds. The 

 overlying masses are limited to the southern section of the 

 island, while dikes occur everywhere, not, however, with the 

 same frequency in all parts. On this subject Professor 

 Phillips was, we believe, the first to offer a good generaliza- 

 tion " Dikes are most abundant at some distance from the 

 granitic centre. At Corriegills, at Lamlash and Tormore, 

 they are exceedingly abundant in the red sandstone, while 

 in the north-eastern face of the island, where that rock is 

 nearer to the granite, fewer dikes appear; and about Loch 

 Ranza the slate is still less divided by them. Perhaps we 

 may venture to add another generalization, viz., that these 

 dikes are most abundant beyond the line of violent flexure 

 of the strata from their horizontal position. After measuring 

 with care the directions and breadths and noting the 

 characters of forty -four dikes, chiefly of gieenstoue, between 

 Brodick and Lamlash, and also those at Tormore, it did not 

 appear to us that any other dependence of the direction of 

 these dikes upon the local centre of the granitic eruption 

 could be traced." (Man. o/Geol., 1855, p. 505.) 



Rocks of the felspathic type, which are most closely allied 

 to granite, seem to have no more intimate relation to the 

 granitic centre than have those of the hornblendic or augitic. 

 The largest body of porphyry on the island is that on the 



