McHknry— /?e/;or^ o?i the " Dingle Bed " Hocks. 23 1 



Beds " at Sybil Head, that they are " quite the same iu mineral aspect as 

 those forming Black Head, south of Dingle," which form the " Parkmore 

 Conglomerate " zone of the " Dingle Beds." 



All round the areas of Wenlock and Ludlow Beds on the north, and north- 

 west, the " Dingle Beds " occur rising from beneath them. But on the south 

 margin they appear to overlie the Ludlow and Wenlock strata. This is due, 

 I hold, to inversion of the strata, as suggested in the accompanying section. 



So far no direct fossil evidence has been forthcoming to prove the possible 

 Llandovery age of the " Dmgle Beds " ; but it is an important fact that in the 

 conglomeratic beds, towards the lower portions of the " Dingle Beds," rolled 

 pebbles of fossiliferous Lower Silurian limestone and grit are found in con- 

 siderable abundance, in what has been named, by the Geological Survey, 

 " Parkmore Conglomerate." Those limestone pebbles have undoubtedly been 

 derived from the Annascaul rocks lying to the south along their margin, and 

 on the north from similar rocks now overlapped and concealed by Old Eed 

 Sandstone, as shown on the diagrammatic section : and they were deposited 

 amongst the overlying and succeeding " Dingle Beds " (probably Llandovery) 

 during their deposition on the eroded and worn-down surface of the Lower 

 Silurian rocks. (See Survey memoir, pp. 16, 17, 33.) The limestone, which 

 belongs to the " Annascaul Beds," is to be seen in situ at a couple of places 

 high up on the western slope of Caherconree mountain. It is identical in its 

 characters with the Lower Silurian limestones of Portraine and Lambay, 

 County Dublin, the Chair of Kildare, County Kildare, and Tourmakeady, 

 County Mayo, and contains similar fossils, a list of which is given in the 

 Survey Memoir, p. 12. The occurrence of the Trilobite Acidaspis Jamesii 

 and other Silurian forms in this limestone is alluded to by Professor Jukes, 

 as " seeming to indicate that the rocks belonged to the Bala group, a part of 

 the Lower Silurian series" (Survey Memoir, p. 12). Specimens of this 

 fossiliferous limestone, and of the fossiliferous limestone pebbles out of the 

 "Parkmore Conglomerate" of the "Dingle Beds" are in the Geological 

 Survey Collection, in the National Museum. 



The belt of rocks ranging from Minard Bay, by Annascaul to Caherconree 

 mountain, have been provisionally designated " Annascaul Beds (Bala or 

 Llandovery rocks) " on the Geological Survey map. From their close 

 resemblance to the Bala limestone and black graptolitic shales and other rocks 

 of Ordovician types in Counties Dublin, Kildare, and Mayo, I have no doubt 

 they are of similar age, i.e.. Lower Silurian. When this region was being sur- 

 veyed over fifty years ago, and subsequently re-examined in 1878, the great 

 importance and efl'ects of inversion and overthrusting were not realized to 

 their full extent. Had it been, I have no doubt the true geological reading 



