250 8. Hyde — Deep-mining in the South-west of Ireland. 



been protruded througli, but which, still underlie, traverse, and 

 affect the Devonian slates (Killas) and grits of Cornwall, do not 

 occur in the south and south-west of Ireland, and therefore the 

 highly mineralized condition of certain zones or areas in the former, 

 metamorphosed and influenced by these rocks, cannot be expected in 

 Ireland. But it is our object to show, nevertheless, that the stratified 

 rock masses of the two peninsulas are of one age, and extensively 

 partake of the same general structure. 



On Pal^ontological grounds we have no means of correlating the 

 Kerry series with Cornwall or North Devon ; the beds in the former 

 area being almost if not entirely unfossiliferous ; in Cornwall also 

 few or none occur. 



I adopt therefore for the Irish area the received canon " that all 

 rocks which were formed after the uppermost of those which can be 

 properly called Silurian, and before the lowest of many wliich can 

 properly be called Carboniferous, may be classed as Devonian rocks, 

 and regarded as rocks of Devonian age." The same is admitted 

 for the rocks of Devon and Cornwall, because the organic remains 

 they contain hold an intermediate place between the true Silurian 

 and true Carboniferous periods. That they lie below rocks of true 

 Carboniferous age is clearly shown along the strike of the Upper 

 Devonian beds, from Croyde Bay to Barnstaple, etc. ; all south of 

 this being the equivalent of the Carboniferous Limestone and the 

 Coal Measures, and, as before stated, the base of the Lower Devonian 

 is not known or seen in North Devon or Cornwall. 



The complete difference in lithological aspect of the two typical 

 Old Eed or Devonian areas, north and south of the Bristol Channel, 

 has been ably described by Sir E. Murchison and Professor Sedgwick, 

 Professors Phillips and Jukes, and later still by Mr. J. W. Salter and 

 Mr. Etheridge ; the latter, in an almost exhaustive memoir upon 

 Devonian Geology, has discussed the whole question. 



The Devonian Eocks everywhere south of the Bristol Channel con- 

 sist of clay slates (killas), red, brown, and gray sandstones, with large 

 masses of limestones occurring at intervals through the middle series ; 

 while the Old Eed Sandstone north of the Bristol Channel consists 

 chiefly of red sandstones, clays, and conglomerates, with no slates or 

 limestones ; they are, nevertheless, of the same age and parts of the 

 same formation. It does not, however, follow that the two groups 

 should be strictly contemporaneous in time. 



It has already been stated that the Upper Silurian Eocks occur 

 in Kerry (Dingle Promontory), where they are covered unconformably 

 by the overlying Old Eed Sandstone, which is some 4,000 feet in 

 thickness ; the underlying Silurian dip south 50° to 60°, and they com- 

 prise the great mass of Mounts Eagle and Brandon. This gives a 

 base for the higher rocks, which lie on and roll in anticlinal and syn- 

 clinal axes, through the three promontories south-east of Dingle Bay. 

 The strike of their axes is north-east and south-west, and seems to 

 be coincident with, or follow, in this sense, the direction of the great 

 planes of deposition, subsequently disturbed along their mean strike ; 

 and most of the faults, where they do occur, are at right angles to 



