GEOLOGICAL SOCIETY OF DUBLIN. 117 



boniferous Slates, and two Old Bed Sandstones ; but I need scarcely 

 repeat that every duplicate band on the low, is also an equivalent of 

 the corresponding band on the high, side. 



Although there is no geological fact in the west of Ireland more pal- 

 pable than this, that the base of the millstone grit to the north of Lough 

 Erne, near Pettigo, stands on a level 1000 feet lower than at Shean 

 Hill, on the south of it, yet this fact seems altogether to have escaped 

 Mr. Griffith's observation. Had he noticed this feature, he would have 

 been able to account in another way for limestone occurring on a low 

 level at Ballyshannon, and high at Dartry mountain, without calling the 

 first lower limestone, and the second upper ; thus making two bands 

 where there is actually but one, and, filling up the intermediate space 

 with an imaginary creation, a band of calp 1 700 feet thick, giving it a 

 false position and a technical name. He would have seen that there is no 

 more reason for those upper and lower limestones than there is for the 

 millstone grit at Pettigo and that on Shean Hill being called lower and 

 upper millstone grits. In both cases they are geological equivalents, 

 or dislocated portions of the same groups of beds. 



It so happens in the vicinity of Bundoran that the two Carbonife- 

 rous Slates, with the upper part of the Old Eed Sandstone between them, 

 come in contact at the surface, partly by ordinary succession, and partly 

 by juxtaposition (see Plate VI., Pig. 5). These three bands, in the po- 

 sition in which they occur, appear to have suggested the origin of the 

 calp, that is, two bands of black shale with a band of sandstone between 

 them, as described at the quotation No. 7, and shown on the explanatory 

 sections on the large and small " Geological Maps." Be it remembered 

 that those three bands do not occur in any vertical section. They are 

 spread out over about two miles of ground. The two upper bands are 

 in succession, as in all other places. The eastern band of Carboniferous 

 Slate is not another band, but the equivalent of the western, separated 

 by dislocation. 



Prom these statements it will be seen that by my interpretation of 

 the facts visible about Ballyshannon and Bundoran, Mr. Griffith has 

 mistaken the succession in the stronghold of his calp ; and, if my views 

 be correct, the whole band of 1 700 feet in thickness must vanish, and 

 be distributed to other divisions of the formation. 



It might be supposed that nothing but the most undeniable testi- 

 mony would be put forward as a basis for a new band or subdivision of 

 a rock formation, and that when this band of Calp, which was not 

 known in the world before, was stated to exist between two limestones, 

 there ought to be a reference made to some place where such band might 

 be seen in its natural position, with the limestone above and below it in 

 direct contact, and in a section which could not be disputed. Such a 

 sight is nowhere in Ireland to be found, — where there is lower lime- 

 stone, there is no upper in the same section; where there is upper, 

 there is no lower. There is no lithological mark in colour or texture 

 by which the volume of the lower can be known from the upper. The 

 fossils are the same in both. In fact, the two are similar in every 



