44 GEOLOGY OF ARRAN. 



above their level, and introduced the temperature and general 

 conditions which, while proving destructive to many species, 

 favoured the immigration and development of that assem- 

 blage of species by which the marine fauna is now distin- 

 guished. But the present level of the shores was not yet 

 attained, nor the actual coast outlines as yet carved from the 

 rocky border which broke steeply down all round the island. 

 The sea covered the plains of Brodick and Shiskin, and 

 stretched its winding arms far up the solitary glens. During 

 the slow progress' of perhaps forty centuries, the streams 

 from the rugged mountain sides and gentler hill-slopes bore 

 down detritus of granite-sand, slate, and quartz pebbles, and 

 spread them out below the waters of the quiet friths. In 

 sheltered places, the tides and waves cut a low but well- 

 marked margin along the highest water line ; while on the 

 open shores the heavier surge wore deeper, the hill-slopes 

 were cut into a steeper and higher cliff, and hollowed out 

 into caves in all the rocks alike. The testacea and other 

 denizens of the present shores already inhabited the waters 

 of that remote period ; but we have no evidence that man 

 had yet appeared. It is most probable, indeed, that the last 

 elevation of the land, to which we have already often 

 alluded, took place before the human period. We are only 

 certain, however, that all the existing levels were established 

 prior to the Roman invasion. Here, as generally in the 

 West of Scotland, this last elevation amounted to about 

 forty feet, and gave to Arran its present maritime border, 

 and the inland cliff which forms a singularly picturesque 

 feature in its coast scenery (see fig. 1, p. 2). 



Shell Beds. 



21. The occurrence of recent shells of arctic species in the 

 deposit called the " boulder-clay," shews that in Arran, as on 

 the mainland, a climate prevailed favourable to the develop- 



