100 



EXCURSION II. 



THE CORRIEGILLS SHORE. 



70. TO-DAY we shall stroll leisurely by the sea-side, and study the 

 eruptive rocks which break through the Corriegills sandstone. The 

 botany of the shore is rich, and the pools in the tide-way teem with 

 marine life. We shall notice in this place the geological phenomena 

 only. A group of whin dikes marks the first emergence of rock from 

 beneath the Brodick sands; and from this point eastwards the rocky 

 platform exhibits a complete network of interlacing veins and beds 

 of igneous products, traversing the sandstone strata. Between the 

 end of the sandy beach and the landing-pier at Spring-bank there are 

 several cases of bifurcation of dikes, and of a singular crumpling of the 

 sandstone strata. The bed of the burn within the pretty grounds con- 

 nected with the hotel shows several greenstone dikes, and the beds 

 of sandstone are well seen in the banks and rocky ledges over which 

 the water tumbles. On the shore fine sandstone and conglomerate 

 are irregularly intermixed, indicating periods of sudden and gradual 

 deposit, and varying forces in the transporting currents. The sandy 

 strata are red, yellow, and white, and, as we advance eastwards, pre- 

 dominate over those of conglomerate structure. The fragments in 

 the conglomerate are mica slate, like that of Cantire, slate similar to 

 that of the nucleus, white quartz, and quartz of that peculiar 

 resinous variety (Art. 47), for which we know no locality in Arran or 

 elsewhere. Pieces of porphyry also occur, but no fragments of 

 granite. The whole series dips nearly south, at angles varying from 

 15 to 20. The upper surface of the sandy beds is worn in a 

 singular way, portions more quartzose, or with a calcareous cement, 

 standing out in thin, sharp, irregular ridges, while the parts around 

 are worn away, being softer or more ironshot. The rock has thus 

 a honeycomb structure, like what one often sees in the worn coral- 

 lines of the mountain limestone. Numerous bowl-shaped cavities 

 also occur, due, probably, to the removal of imbedded quartz balls, or 

 the grinding action of these, by the movements of the waves, when 

 once loosened from their bed in the sandstone. 



Some general remarks have been already made (Art. 57) on the 

 dikes of this coast, and we shall now only notice the individual cases 

 of most interest. The whole number is about sixty, and the direction 

 generally between N.W. and N.E., a few running nearly E. and W. 



