172 Mr. Griffith, on the Order- of Succession of the Older 



limestone, and underlying black carboniferous slate, inter- 

 stratified with thin beds of limestone, which is ultimately 

 succeeded by limestone without admixture ; the whole of the 

 strata dipping to the south. Again, on the south side of the 

 river Roughty, immediately to the east of Roughty Bridge, 

 a similar succession of strata is observed dipping to the north. 

 In this locality, the'yellow sandstone contains that variety of 

 calamite which is characteristic of the rock, and which is also 

 abundant at Brickeen Island, near Killarney, and in the same 

 geological position, underlying the limestone of the several 

 troughs of the counties of Waterford and Cork. In the car- 

 boniferous slate of Roughty Bridge, Retepora memhranacea 

 was observed. I shall mention one other locality in which 

 the strata in connexion with the yellow sandstone have been 

 observed in the valley of the river Roughty, namely, at the 

 pier at Kenmare. At low water in this place, gray quartz rock 

 and black carboniferous slate may be observed dipping to the 

 north under the lower beds of the carboniferous limestone, 

 which are exposed to view in an adjoining quarry. Imme- 

 diately to the south of this quartz rock and slate, no rocks 

 are visible, the strata being concealed by sand; but in a very 

 short distance, beds of yellowish green slate, alternating with 

 red slate and red limestone, occur which are identical with 

 the strata visible in the localities already mentioned under- 

 lying the yellow sandstone : no doubt can therefore be enter- 

 tained that this rock is continuous on the south side of the 

 valley from Kenmare pier to Roughty Bridge. It is true, in 

 this locality, as well as in most others, that the yellow sand- 

 stone has not been seen at the surface throughout the entire 

 length of the carboniferous limestone trough, as, owing to 

 a thick covering of diluvial matter, or of bog, the precise 

 boundary between the base of the limestone series and the 

 old red sandstone rocks is rarely visible; but as the yel- 

 low sandstone and dark gray carboniferous slate do occur 

 in every place where the outer boundary of the limestone 

 series is exposed to view, I feel little doubt that these rocks 

 equally occur in those positions where they are concealed from 

 our view. If geologists were only to mark the limits of their 

 rock districts in the precise localities in which the contacts 

 are visible, no geological map could be formed. In maps on 

 a large scale, the observed contacts might be shown by con- 

 tinuous, and the supposed by dotted lines : but on a general 

 map, though desirable, it would be impossible to enter into 

 such detail, or if attempted it would be impracticable, on a map 

 on which the features of the country are shown, to distinguish 

 between the continuous and the dotted lines. 



