34 GEOLOGY OF ARRAN. 



centres." A similar idea would be very likely to occur on 

 examination of M. Necker's map, which certainly Mr. Napier 

 had not seen, else he would have mentioned it. The notion 

 of radiation from a common centre we do not, however, find 

 alluded to in M. Necker's paper. Mr. Napier seems dis- 

 posed to assign two centres one for the felspathic dikes, and 

 another for the hornblendic both lying inland towards the 

 Lamlash road. Prolonging the directions of the two prin- 

 cipal felspathic dikes on the shore, he finds that they would 

 meet near the claystone quarry on the Lamlash road, about 

 a mile from Springbank ; and here he would place the fel- 

 spathic centre; the hornblendic he does not so definitely fix. 



Now, analogies in support of this view can certainly be 

 drawn from districts of recent volcanic action, where fissures 

 radiating from a vent, or focus of disturbance, are seen to be 

 filled with basaltic lava and other igneous products; and the 

 same may doubtless have occurred in the case of the plutonic 

 rocks ; but the evidence for it in Arran we cannot consider 

 sufficient There are many exceptions to the rectilineal* 

 course of dikes here as in other places; some of the dikes 

 converge towards the Corriegills shore, and the largest runs 

 a long way parallel to it, while one at least re-appears far 

 inland beyond the place of the supposed focus. Besides, so 

 far from " the whole of the hills between Brodick and Lam- 

 lash being composed of trap," this rock is, in point of fact, 

 confined to a narrow and thin capping along the highest 

 ridge between the two bays; and Mr. Napier has overlooked 

 the great outburst of porphyry at Dunfion, which has a 

 manifest relation to the felspathic dikes on the shore, as well 

 as the numerous masses of claystone intercalated amongst 

 the sandstone strata along the northern slopes west of 

 Corriegills. 



On these grounds we cannot admit that this speculation 

 has much value ; the apparent radiation arises from the cir- 

 cumstance already mentioned, that the vast majority of the 

 dikes range between the points of extreme magnetic declina- 



