S. Hyde — Deep-mining in the South-ivest of Ireland. 249 



Tho correlation of tho rock masHos of the south of Trolaiid, OKpocially 

 those of Kerry and soulli-west Cork, have been a difliculty with many 

 distinguished geologists ; and tho relation they liold to tho so-called 

 Devonian series of north Devon and Cornwall is even now a dis- 

 puted question with many. 



It is thcroforo very important to understand the relation of tho 

 two mining areas, which occujiy a similar googra})hical position in 

 both promontories, viz., that of south-west Ireland and south-west 

 England. It is true the succession of the Palssozoic series is clearer 

 and better developed in the south-oast, south-west, and central Ire- 

 land, than in Cornwall; the Old Eed Sandstone of Ireland being 

 known to repose upon the Upper Silurian series of the Dingle pro- 

 montory, and upon the Lower Silurian in Waterford. 



In Cornwall and Devon, on the contrary, no Upper Silurian rocks 

 of either of its sub-divisions are known ; and the Old Red Sandstone, 

 or Devonian series of the English peninsula, have no known base, such 

 having never been determined in its tjrpical areas, viz., north and 

 south Devon and north Cornwall. This problem has yet to be 

 solved, and the determination of Upper Silurian rocks, south of Pem- 

 brokeshire, holding some relation to the Linton and Ilfracombe series 

 in north Devon, or to the same series that constitute the structure of 

 the west coast of Cornwall, from St. Agnes Head to Tintagel and 

 Boscastle, would perhaps decide their relation to the Devonian rocks 

 of Kerry and south-west Cork. 



It is true we have at Bolt Head and Start Point, in the south of 

 Devon, a series of Crystalline Quartzite rocks, believed to be of 

 Silurian age, and some equivalent beds at Mevagissy and the Dodman, 

 in east Cornwall, but whether they are equivalents of the Cambro- 

 Silurian series (Caradoc and Llandeilo) of east and central Ireland is 

 doubtful. Whatever may be the age of the Start and Dodman rocks, 

 they are the only representatives of the Silurian series in Devon and 

 Cornwall, being mere remnants of a once largely spread group to the 

 south, originally connecting the Palseozoic rocks of Brittany, or 

 north-west France, with south-west England. 



The details of the Devonian system in the two countries seem to 

 involve rather a question of terms, than difference as to age ; though 

 in an economical, mineral, or mining point of view, it is extremely 

 desirable that the relationship of the group of rocks occupying the 

 two areas should be cleared np. If this cannot be done strati- 

 graphically, it is hoped some light may be thrown upon the 

 question by deep-mining in Ireland, and a knowledge of the 

 deeper physical aspect and structure of the Irish rocks arrived 

 at by comparison with those of the Cornish area. Also, the intimate 

 structure and conditions of the lodes and their contents, such as 

 the mode of infilling and arrangement of their mineral contents, 

 systems of underlay, directions or bearing, etc., nature of the 

 cross courses and true relation of the Irish El vans to their own 

 rocks and minerals, as well as to those of Cornwall, at present very 

 little understood. 



We are aware that the great masses of igneous rocks which have 



