Mr. G. S. Kinahan — Irish Carboniferous Rocks. 521 



of the difficulty. I should feel much grieved if these remarks 

 appeared to convey any slight whatever on the careful work of 

 modern palaeontologists ; but my impression is that the object of 

 their labours will be to a sei'ious extent frustrated if their results 

 are published in too complex a form for the " general geologist." 

 Having said so much about changes of names, perhaps I may be 

 pardoned if I sign myself, Eob. W. Haddow. 



. Banbuky, Uh Sept. 1887. 



CHERT IN IRISH CARBONIFEROUS ROCKS. 



Sir, — Chert is not, as supposed by Dr. Hinde, a definite character- 

 istic of the Irish Upper Carboniferous Limestone (see chapter v. 

 Manual of the Geology of Ireland, C. Kegan Paul & Co., 1878). 

 Where this limestone is fully represented as in Co. Limerick, etc., 

 the " lower cherty zone " is thei'e best developed ; and it occurs in 

 the lower limestone, between the " lower shaly limestone " and the 

 " Fenestella Limestone." A second conspicuous zone for chert lies 

 between the Fenestella Limestone and the upper limestone, when of 

 the " Calp type." In the upper limestone of Cork and Kerrj^ there 

 are layers and nodules of chert, but in Limerick, Tipperary, and 

 part of Galway it is rare, while in the rest of Galway and in Clare 

 it is more common. In part of Leinster, between the upper lime- 

 stone and the Coal-measures lower shales, there is a cherty zone, 

 but in the rest of Leinster and in Munster in all the known sections 

 of the junction of the Limestone and Coal-measure shales, this 

 cherty zone is absent. In Ulster, however, especially Fermanagh, 

 where sections can be seen, this cherty zone is well developed and 

 of a character similar to that described by Dr. Hinde as characteristic 

 of the Yoredale Series, Yorkshire. 



According to my experience cliei't is as frequent, if not more so, 

 in the Lower, as in the Upper Irish Carboniferous Limestone. When 

 it occurs in zones, it is usually accompanied by shaly beds, and is 

 more or less friable ; but when in compact limestones like those of 

 the " Burren type," it stands out conspicuously like the nodules, 

 lentils, and layers of flint in the chalk, as can be seen in innumerable 

 places in Cork, Kerry, Clare, Sligo, Fermanagh, etc. ; near Athenry, 

 Co. Galway, in a railway-cutting, there is a thick bed. 



As Dr. Hinde has been making researches as to the origin of 

 chert, I would specially direct his attention to the chert lentils 

 perpendicular to the stratification in Benmore, Co. Fermanagh, to 

 which attention was first drawn by Thos. Plunkett, M.R.I.A., of 

 Enuiskillen, in a paper read before the Royal Dublin Society. Those 

 mentioned in his paper occur in Benmore, but I have since observed 

 them in Belmore and other places in that county. They are lenticular 

 masses in height and depth, and have all the appearance of ordinary 

 chert. I take it that they are the filling in of shrinkage fissures 

 along a line of partial rupture. I would also draw his attention to 

 the lower and middle cherty zones in the Co. Limerick, both of which 

 are remarkable Palgeozoic breaks, as in the intervening rock, " Fenes- 

 tella Limestone," the fossils are quite distinct and much more 



