372 



Proceedings of the Royal Irish Academy, 



These divisions consist of quartzite at tlie top of the series, then a 

 pebbly or conglomerate zone ("Boulder Bed"), which passes do-wn 

 into a limestone that is sometimes also pebbly. Associated with the 

 limestone, and mostly below it, comes a series of black shales and 

 grits, the shales being sometimes graphitic, and the lowest of all a 

 great series of pebbly grits, with occasional thin black shale or schist 

 beds, which in the south-western extension of the series north of 

 Castlebar, around "Westport, and along the south shore of Clew Bay, 

 have been locally designated by myself and my colleague, Mr. Kilroe, 

 as the "■ "Westport grits." 



Sheared pebbly grit (quartzite) cut by early basic (B.) and later acid granulite 

 rocks (C), the whole series having been subjected subsequently to still 

 later shearing. 



"West side of Derryclare Lake, Connemara. 



This metamorphosed sedimentary series has been extensively 

 invaded by a complex of basic and acid igneous materials, and shows 

 great alteration both by contact with the igneous intrusions, and the- 

 later earth stresses that probably accompanied, and evidently succeeded, 

 those intrusions. In many places the limestone, where it has been 

 invaded and enveloped by the acid igneous masses, is converted into a 

 whitish saccharoid marble with garnets developed in it, exactly like 



