116 



Proceedings of the Royal Irish Academy. 



Dingle series points to erogenic movements of an earlier date ; these 

 appear to have been obliterated almost wholly by the movement of 

 later times. 



Of the igneous rocks associated with the sedimentary series, we 

 can say very little. Tour small masses are indicated on the map ; but 

 none of these was found fresh enough to merit a petrographical 

 description. Three of them behave as sills, and are more or less 

 altered sub-acid felsites or acid andesites, and seem at one time to 

 have contained small porphyritic crystals of brown biotite. One of 

 these, occurring at the edge of one of the synclines, behaves as one 

 might expect a rock to do if intruded at or about the time of the 

 folding ; but, on the whole, we are inclined to regard all these sills as 

 being connected with the hypersthene andesites of the Old Red Sand- 

 stone of Sentry-box Hill, four miles to the south. The relations of 

 the fourth intrusion, a dyke cutting the isoclinal folds transversely in 

 the Little River, west of Mullaghnabuoyah — are more obvious ; and 

 this is probably the newest rock in the district. It is altered beyond 

 all hope of recognition, and now consists only of the three minerals — 

 quartz, calcite, and shining cubes of pyrites. The great bulk 

 of the rock consists of granular secondary quartz, with sutured 

 junctions. The calcite occurs in granular pseudomorphs, which have 

 the shapes and habit of short prisms of hornblende, though some may 

 also represent crystals of porphyritic felspar. The distribution of 

 the pyrites is sporadic ; and the displacement of the other materials 

 around its crystals is obvious. 



Comparison with the Lower Falceozoic Rochs of other Areas. 



As might be expected, the Ordovician and Silurian rocks of 

 Pomeroy find their closest parallels in the contemporaneously-formed 

 rocks of South Scotland ; but whereas the Desertcreat group finds its 

 nearest allies in the rocks of Grirvan, the beds of the Little River group 

 are more closely related to their equivalents at Moffat. 



Taken as a whole, the Desertcreat group seems to be the equivalent 

 of the Drummuck group at Girvan ; and it would appear quite possible 

 to trace even minor divisions through the two areas. The pebbly 

 flagstones of Quarrel Hill at the latter place, with their abundant 

 Strophomenas, are the Bardahessiagh beds, but, though conglomeratic, 

 are never seen to rest upon other than Ordovician rocks. The Trinucleus 

 mudstones which succeed are exceedingly like the KilleyJBridge beds, 



