148 



Pi'oceedinfjs of the liotjal Irish Academy. 



south of Maam Hotel, near the public road. These coarse, pebbly, or 

 conglomeratic bands correspond in character and zonal place in the 

 metamorphic series with the coarse, highly-altered grits and conglo- 

 merates at Westport and to the north of Castlebar. 



The remarkable way in which the rocks of this area have been 

 a:ffected by earth-stresses is well illustrated by the manner in which a 

 band of mica-schist, which does not appear to have been originally an- 

 igneous intrusion, has been thrust up iuto the quartzite ridge trans- 

 versely to the prevailing strike, one and a half mile south of Pollna- 

 cappul Lough at Kylemore : the present foliation is parallel to the 

 walls of quartzite on either side ; and a further illustration is found 

 in a peculiar occurrence of the boulder-deposit in Maam Gap. Here 

 large, roundish boulders of reddish granite are enclosed in a greenish- 

 gray highly micaceous grit, forming a mass resembling the boulder- 

 deposit near Recess ; ^ and it is here bounded east and west by the 

 quartzite of the range, on the south by a granite which invades it 

 and the quartzite, and on the north by gray mica-schist, which, 

 though stratigraphically lower in the series, i.e., older, seems to have 

 been pushed southward over it and over the quartzite. The boulder- 

 deposit being here over-ridden by the mica-schist and limestone group, 

 may suggest the reason for the non-appearance of the former where it 

 might be expected along the north side of the range between the 

 quartzite and mica-schist. 



It may be noted that the overfolding "creep," attended with 

 shearing and foliation of the rocks, was from the K.N.E. in this 

 region— repeated, as we shall see later on, in post-Silurian times ; 

 while the creep was from the S.E. north of Clew Bay, and from the 

 E.S.E, and south at Glencalry and Kilcommon. 



In concluding this account of the Dalradian series of North Galway, 

 reference should be made to important outcrops of igneous rocks which 

 form in great part the rugged platform overlooking Kylemore on the 

 north. Attention was called in the original Survey Memoirs and 

 maps to the great mass of hornblende rock on the summit of the 

 escarpment which terminates the platform ; but invading this is a 

 granite-gneiss, in parts quite coarsely crystalline, which is repre- 

 sented on the published maps as metamorphosed Lower Silurian strata, 

 though on the 6-inch working maps it is justly described as fine and 

 coarse gneiss. At the time this ground was being mapped the hypo- 

 thesis prevailed that granitic gneisses mark the last stage but one^ 



1 Described in Appendix to 43rd Rep. Dept. Sci. and Art (1895), p. 36. 



