Kinahan — On Irish Marbles and Limestones. 377 



that will be most intelligible, especially when the correct definitions 

 -of the names are also given. 



Other Carboniferous limestones are those that occur as the 

 basal beds of the Carboniferous rocks, associated with the con- 

 glomerates, in the counties of Clare, Galway, and Tipperary. 

 These, however, are of minor importance, and appear to have been 

 but little utilized. 



There are also limestones that occur at the margin of the 

 Ordovician (?) or Cambrian (?) metamorphic rocks to the north- 

 ward of Castlebar, Co. Mayo, which Symes suggests are of Car- 

 boniferous age (Geol. Surv. Mem.). His arguments cannot be 

 lightly passed over; the principal ones being that these limestone 

 are unconformable to the associated rocks, that they occur in more 

 or less dyke-like masses, and that they are devoid of the characters 

 of metamorphic limestone. An examination of the rocks seems to 

 prove that they must be much more recent than the adjacent meta- 

 morphic rock, and that they are of Silurian or Carboniferous, or 

 even of a later age. Symes, after his examination, suggested that 

 they were Carboniferous, and due to the filling in of open fissures, 

 during that period, with Carbonifereus matter. It is, however, 

 possible, as has been suggested by myself, that these fissures were 

 filled in by Silurian limestone. To this we shall refer presently. 

 All these limestones are more or less used for lime, some of them 

 being hydraulic. 



In the Silurian group (which includes the rocks that hare been 

 called Upper Silurian and Lower Old lied Sandstone) limestones are 

 rare, and occur in beds of small dimension. They have been 

 recorded in the following places: — At Croaghmartin, in the Dingle 

 promontory, Co. Kerry, are some insignificant arenaceous lime- 

 stones. In the Co. Galway, at Salrock, Derreennasliggaun, and 

 Leenaun, there are small subordinate masses of limestone, those at 

 Derreennasliggaun being in part somewhat coloured red. Farther 

 eastward, partly in the counties Galway and Mayo, are peculiar 

 limestones, associated with the eruptive rocks that occur at the 

 base of the Toormakeady conglomerate. These rocks are very 

 interesting, as they may possibly be of the same age as the lime- 

 stone northward of Castlebar, which, as suggested in the previous 

 paragraph, may be either Carboniferous or Silurian. South-east- 

 ward of Louisburgh, in S. W. Mayo, there are thin limestones, in. 



