374 



Proceedings of the Royal Irish Academy. 



Interbedded Tvith. those pebbly grits, there are black shales, which 

 but for the amount of deformation, through movement in the rock 

 masg that they have undergone, are closely similar to Ordovician 

 shales, from which fossils of Llandeilo types have been obtained. 



Of the two varieties of igneous intrusions, the basic is the earlier, 

 abundant and conclusive evidence existing at many points to prove 

 this fact (fig. 1). After the basic came an acid intrusion which 

 affected both the basic igneous and the sedimentary rocka to a 

 considerable extent, large masses of both these (basic rocks and 

 sediments) in a highly mineralized condition being included in the 



Fig. 3. 



(C.) Acid granulite enveloping sediments (A.) and early basic igneous rocks (B.), 

 ■with later uncrushed granite (G.). 



Xear Maam Cross, Connemara. 



granulitic or second igneous intrusion (fig. 2). Subsequent to the 

 period of this acid intrusion, intense earth stresses took place, which 

 resulted in a milling out, shearing, and banding of all three varieties 

 of rock, thus forming those banded gneissose rocks and sheared or 

 bedded-like rock -masses as they now exist, and which were considered 

 by some authorities to be metamorphosed early Palaeozoic sediments, 

 and by others to belong to a more ancient or Archaean period. 



