258 mOF, E. HULL ON THE GEOLOGICAL RELATIONS 



greenish, and reddish sandstones and shales, with fish (Ast 

 Bothriolepis, Glyptolepis, Coccosteus, and Pterichthys), also Ano- 

 donta Jukesli and plants {Adiantites, &c.) : (b) the above passing 

 down into massive reddish-brown and purple soft sandstone with a 

 conglomerate base *, the whole about 3000 feet thick. 



The basal conglomerate of the Old Eed Sandstone is everywhere 

 unconformable to the rocks on which it rests over the South of Ire- 

 land, as frequently insisted on by the late Sir E,. Griffith f. This 

 unconformity is equally conspicuous, whether it refers to the con- 

 tact of the conglomerate with the Uppermost Silurian beds in the 

 promontory of Dingle, or to the Lower Silurian beds of the Come- 

 ragh or Galtee Mountains. On the other hand, all the beds from this 

 conglomerate upwards into the Carboniferous Limestone are appa- 

 rently in perfect conformity with each other, notwithstanding the 

 change from the apparently fresliwater " Kiltorcan beds " into the 

 marine '^ Coomhola-Grit series " which succeeds to them. The 

 hiatus in the South of Ireland is therefore at the base of the Old Red 

 Conglomerate. 



lY. Division between the Caebonifeeotjs and Old Red Sandstone 



EOKMATIONS. 



A recent author has included the Old Eed Sandstone of the south 

 of Ireland in the Carboniferous group, on the ground that " in no 

 place in Ireland has it a defined upper boundary, one group gradu- 

 ating into the other "J. Although this view finds some support, if 

 the purely strati graphical relations of the two series alone be re- 

 garded, yet it seems to be untenable upon palaeontological and phy- 

 sical considerations, to which sufficient weight has not been allowed 

 by the author above quoted. In the first place, the occurrence of 

 Ayiodonta, together with the absence of any traces of marine organ- 

 isms, seems to point conclusively to the lacustrine origin of the upper 

 beds at least (" Kiltorcan beds ") of the Old Eed Sandstone ; on the 

 other hand, the moment we pass upwards into the slates and grits 

 of the overlying " Coomhola series," we are met by abundant evi- 

 dences of the prevalence of marine conditions in the occurrence of 

 such genera as Avicula, Cucullcea, Modiola, Mytilus, Rliynchonella^ 

 and Sjnrifera, and other forms which connect these beds with the 

 Carboniferous system. 



Again, the occurrence in the Kiltorcan beds of the remains of fish, 

 belonging to recognized Old Eed Sandstone forms, both in Scotland 

 and elsewhere, such as Asterolepis, Bothriolepis, Glyptolepis, Cocco- 

 steus, and Pterichthys, none of which ascend into the Carboniferous 

 series of other districts, or into the Carboniferous-Slate series of 

 Ireland, places the relations of these beds to the Old Eed Sandstone 

 beyond question. In fact, it is abundantly clear that lacustrine 



* This great conglomerate is well shown in the banks of the river Suir at 

 Waterford, and the escarpments of the Oomeragh Mountains in Co. Water- 

 ford, and of Caher-con-ree in the Dingle promontory. See Section I. sheet 13, 

 of the Sections of the Geol. Surv. Ireland, &c. ; also Jukes, Quart. Journ, Geol. 

 Soc. vol. xxii. p. 328. t Journ, Geol. Soc. Dubl. vol. viii. passim. 



\ Kinahan, ' Geology of Ireland,' p. 63. 



