22 GEOLOGY OF AKRAN. 



sandstone of Craig-Dhu, or at the junction of this rock with 

 the carboniferous strata, and also amidst these carboniferous 

 strata at Ploverfield. In each of these positions it must be 

 regarded as posterior to the rock which encircles it, since it 

 is intruded among these sedimentary deposits and produces 

 a marked alteration upon them along the planes of contact. 

 We have, therefore, now to consider the question of age. 

 Are the three granites of three distinct ages coi-responding 

 with those of the strata among which they intrude ? or were 

 they erupted simultaneously, so as to pierce through the 

 three formations during one and the same period of disturb- 

 ance 1 In other words and this view narrows the question 

 since the Ploverfield granite is clearly of later origin than 

 the sandstones of Windmill Hill, and the shell limestones 

 subordinate to them, were the granites of the nucleus and of 

 Craig-Dhu erupted at the same time with it ? or does their 

 injection among the strata, and elevation to the day, date 

 back to an earlier period ? The close proximity of the Craig- 

 Dhu granite to the border of the carboniferous formations, 

 if it be not actually enclosed in these, evidently points to an 

 identity of age with that of Ploverfield, and renders their 

 simultaneous eruption extremely probable. How then is 

 the granite of the nucleus related to the old red and 

 carboniferous formations? It has been long established, and 

 is well known that it everywhere throws powerful veins into 

 the encircling slate-band, greatly altering this rock along the 

 line of junction, producing banding and contortion, and dis- 

 turbing its stratification. In some vertical sections, as at 

 Torneadaneoin, and the hill-sides north of Glen Catacol, 

 we have slate above and granite below, with numerous alterna- 

 tions where the two rocks approach. Hence we infer that 

 the granite was injected in a melted state amid the already 

 formed strata of slate. But, further, it was suggested long 

 ago by Murchison and Sedgwick, in their celebrated paper 

 on Arran (Geol. Trans., vol. iii., second series, 1835), that 

 the bed of limestone on the north front of Maoldon may have 



