O. II. Kinahan — Geologij of Parts, of Galivay and Mayo. 455 



the first of the sheets of felstones was poured out, all the country 

 became submerged ; but in the north country the accumulation 

 partook more of shore depositions ; so that there conglomerates and 

 sandstones are the prevailing rocks, while in the south country there 

 are large thicknesses of argillaceous rocks. 



The Upper Silurian rocks lie unconformably on rocks that are 

 more or less altered. To the north of the Upper Silurian rocks in 

 the neighbourhood of Doolough, and near Lough Mask to the east, 

 the lower rocks are only slightly mineralized, and belong to the 

 rocks called by the Indian Surveyors " Sub-metamorphic." In some 

 of these, fossils are preserved, so that we have been able to determine 

 that the Doolough beds are of Lower or Cambro- Silurian age. To 

 the south of the Upper Silurian rocks the lower rocks are much 

 more altered, some indeed having lost all traces of their sedimentary 

 character, and been changed into different varieties of granite. In 

 none of these rocks, although some to the extreme south, at Letter- 

 muUen, are very little altered, have we been able to detect fossils ; 

 yet we believe they are of Lower or Cambro-Silurian age, and that 

 if disentangled, they would lie in a great undulatory anticlinal curve 

 that sinks towards the east and rises to the west, so that only in the 

 neighbourhood of the Atlantic are the lowest beds brought to the 

 surface. The rocks forming this curve can be divided into groups 

 that are represented in both arms of the curve, and only slightly 

 differ in thickness (see Sections, page 456) : — 



North arm. South arm. 



over 600 feet j3^^ Hornblendite, talcite, and felsitite series over 2000 feet. 



V i ocArt oinfGi-reat micasite series with inliers of) , , „n„n 



about 2500 „ ^io| hornbleade-rock, ophite, steatite, etc. } ^^°^* ^000 „ 



„ 300 „ /3^ Lesser quartzite series „ 100 „ 



,, 1600 „ j38 Lake series containing many limestones... „ 1800 „ 



„ 300 „ /3" Middle micasite series „ 1000 „ 



„ 1000 „ )3S Great quartzite series „ 600 „ 



„ 600 „ fi^ Small micasite series „ 100 „ 



„ 300 ,, ;8* Ophiolite and dolomite series „ 200 „ 



„ 1000 „ j3^ Quartzitic-micasite series „ 1000 „ 



„ 400 „ )8^ Streamstown Bay limestone series ,, 400 „ 



over 100 ,, y3^ Lower micasite series over 100 „ 



8,600 feet. 10,300 feet. 



In the south arm more of the upper rocks yS" are seen than in the 

 north arm, as in the latter place a considerable portion is covered by 

 the Upper Silurian ; but to the north of the latter there* is a vast 

 thickness of the "Doolough beds," which are supposed to be the 

 representatives of y8". The lower Groups /3^ to /3"^ are only positively 

 known to exist in the vicinity of Streamstown Bay, a fiord from the 

 Atlantic, although some of the limestones in the Owenglin Valley 

 may belong to Grroup /3^. Groups /3^ to ^^^ are found in various 

 places, but rarely in consecutive order, as, on account of the innumer- 

 able faults, the same group or groups may be repeated, or one or 

 more groups may be cut out. 



In this country it is evident that the metamorphism is not due to 

 the granite, but that the granite is due to the metamorphic action ; 



