186 Proceedings of the Royal Irish Academy 



The younger Palaeozoic rocks, i.e. the different members of the O.E.S. and 

 Carboniferous systems, very rarely indeed show signs of ice-scratches ; and 

 this fact, together with the great thickness and abundance of the drift deposits 

 in the peripheral areas where these rocks occur, explains the virtual absence of 

 striae in this part of the country — a feature which the accompanying map 

 (PI. IX) renders strikingly apparent. Tet at Muckros, north of Donegal 

 Bay, the coarse Carboniferous conglomerate has preserved its striations both 

 on the constituent boulders of quartz and quartzite, and on the enclosing 

 matrix. 



Roches raotdonnees of all sizes occur in the greatest profusion, especially iu 

 the Donegal mountains, ranging from some of the largest hills in the country 

 down to the small rounded knobs of which hundreds may dot the floor of a 

 small valley.' 



The striae and roches mouionnees afford an extremely complete and 

 satisfactory body of evidence as to the du-ection of movement of the ice-masses 

 in the region under review, and throw considerable light upon the general 

 character of the glaciation. They bear witness to the intensity and persistence 

 with which the ice performed its work. Striae and grooves occur at all 

 altitudes up to the summits of the highest mountains. Generally speaking, 

 they are most plentiful on the flanks and summits of the ridges and hills, and 

 rarer in the bottoms of the valleys and glens. 



Boulder transport and striae directions are also in striking agreement, 

 together forming a consistent system. In all the larger Donegal valleys, 

 with but few exceptions, the direction of the striae and the boulder trains 

 shows that the movement of the ice was along their lengths and generally 

 parallel with the trend of the larger ridges. In some instances the striae 

 indicate the turning aside of the ice, as the result of the deflecting influence 

 of the local topography, the deviation from the general direction being such 

 as a study of the local relief would suggest. On the ridges evidence is 

 occasionally found of the oblique passage of ice across the axes of the valleys, 

 suggesting the movement of the upper portions of the ice in a direction 

 differing from that of the lower parts which were hemmed in between the 

 valley sides. 



Terminal ciu'vature was observed in a nvtmber of places. 



' Where almost every iiTegularity in the surface is a roche montonnee, the use of a 

 special symbol to indicate such would no longer have any particular utility, and such a 

 sign has therefore not been used on the accompanying map. 



