138 The Rev. Maxwell H. Close, 



At Portrane there is, on the shore, a small, but very noticeable, 

 exposure of this formation. The beds are sometimes much con- 

 torted, but their general dip on the shore is towards S. of E. The 

 rocks consist of slates and shales containing graptolites and trilo- 

 bites, with some grits and, more especially, highly fossiliferous beds 

 of limestone; all the fossils being of Bala or Caradoc age. There are 

 also several interstratifled beds of trappean ash, evidently con- 

 nected with the contemporaneous felstone porphyry close by on 

 the YV. and S. There is, in some places, a well defined cleavage 

 whose planes dip about S. 30° E. at 40°. 



Lambay Island is 2'£ miles off Portrane. It is principally 

 composed of felstone porphyry with various small masses of 

 Lower Silurian stratified rock, some probably caught up in the 

 felstone. The slates of some of these yield graptolites. At Kiln 

 Point, on the shore near the S.E. angle of the Island, there is a 

 mass of thin beds of limestone which contain Bala fossils ; they 

 have thin earthy shales between them. The felstone has sent 

 veins and strings into the lowest bed of the limestone ; but it 

 has not had much altering effect thereon. The geological interest 

 of this island is increased by the occurrence, near its N.W. point, 

 of a remnant sheet of Old Red Sandstone (?) not more than 50 

 feet thick. This consists of sandstones above, and a conglomerate 

 below. It extends along the S. side of Broad Bay for a length of 

 nearly one furlong ; the beds dipping N. at from 60° to 30°. 

 The base of the conglomerate is well seen ; it lies unconformably 

 on the Lower Silurian ash and slates, which, at this place dip S. 

 at about 50°, and must be now inverted. The N. part of this 

 remnant sheet is cut off by an E. and W. fault. 



The black slates which occupy the low south-eastern part of 

 Ireland's Eye, and which apparently rest unconformably on the 

 Cambrian rocks, most probably belong to this formation. 



At a few miles southward of Dublin, the Lower Silurian sets 

 in as the surface formation; it extends thence to Waterford 

 Harbour, except that it is interrupted by the Cambrian and 

 granitic exposures. 



The rocks of this Lower Silurian area within the district with 

 which we are now concerned, are unfossiliferous ; but in Wicklow, 

 at Slieveroe, near Rathdrum, and in the Co. Wexford, they have 

 yielded various fossils of Bala or Caradoc type. The small ex- 

 posure of this formation at the Chair of Kildare, twenty-four miles 



