Clare Island Survey — Geology. 7 13 



shales and rough sandstones being ill adapted for retaining these impressions, 

 but the characteristic ice-grooved and ice-planed rocks so often found in the 

 paths of great glaciers are common here also, especially along the southern 

 shore. As already stated, the principal modifications of the rock-surfaces 

 were produced by the glacier from the east. The peculiar ice-dressed rocks 

 known as roches moutonnees are common even at considerable elevations. 

 Thus, on the western coast, south of the lighthouse, a good example of these 

 glaciated hummocks may be seen. Glaciated rocks of this type occur, also, 

 near the signal-tower on the west coast, at a height of 470 feet, and on the 

 east side of Knocknaveen, at a height of 600 feet above Ordnance datum. 

 All these phenomena bear testimony to the great mass of the earlier ice-sheet 

 that swept over Clare Island, as well as to the intensity and persistence with 

 which it performed its work. 



Fine examples of the striae which it inscribed on the rock-floor may be 

 observed at various points along the whole of the southern coast from 

 Ooghnamaddy to Kinatevdilla. With some minor oscillations, probably due 

 to the unevenness of the rock-surfaces over which the ice moved, most of 

 the striations point seawards in a direction a little to the south of west. 

 Well-marked cross-striae, produced by the district glacier coming from the 

 ice-shed of the mountainous country between Clew Bay and Galway Bay, 

 were noted in at least four widely separated localities on the island ; they 

 are oriented in a direction bearing 30° to 35° north of west. 



The distribution in this area of certain distinctive foreign erratics, which 

 cannot be matched with any of the fundamental rocks of the island, is 

 confirmatory of the movements of the principal ice-currents as deduced 

 from the evidence furnished by the manner in which the rocks are glaciated. 

 Thus, boulders of scratched limestone, which are common in the oldest and 

 and most massive of the superficial deposits of the island, must have come 

 in the great ice-stream that flowed westward from the central Irish axis 

 from the limestone area lying to the east of Clew Bay. Also, granite 

 boulders, lithologically identical with the granite of Corvockbrack (situated to 

 the south of Clew Bay), are of frequent occurrence on the southern portion of 

 the island. Massive blocks of this rock, some of which weigh from about half a 

 ton to a ton, were noted along the course of the Owenmore stream on the 

 south-eastern slopes of Croaghmore (Knockmore), and smaller fragments of 

 the same rock appear also, amongst other places, on the top of Knocknaveen, 

 650 feet above the level of the sea. Again, scratched serpentine erratics, 

 identical with the serpentine from Croagh Patrick, are fairly common along the 

 southern coast of the island. Both the granite and serpentine boulders either 

 rest on the surface of the ground, or are embedded in the more superficial 



