1908-1909.] 2II 



"A GOSSIPING GEOLOGICAL SPECULATION 

 ON CAVE HILL." 



At a meeting, held in the Natural History Society's Museum, 

 on Wednesday. 24th March — Mr. W. J. C. Tomlinson in the 

 chair — Mr. William Gray, M.R.I. A., promoted a geological gossip. 

 Mr. Gray said the structural basis of Antrim is mainly the section 

 exposed at Cave Hill, and the rocks that occur along the north 

 coast are the same as the rocks that occur in sections immediately 

 below the highest point of Cave Hill. There is, however, an area 

 of about nine or ten miles square of the north-east of Antrim 

 where the rocks are chiefly metamorphic, and therefore older 

 than any other rocks in Antrim or Down. Next above and 

 reposing upon the primary metamorphic rocks come the extensive 

 silurian beds of County Down, composed of shales, grits, and 

 slaty beds of great variety and fine texture. Reposing upon these 

 silurian rocks we have at Holywood, Castle Espie, and Cranfield, 

 three varieties of fossiliferous carboniferous limestones, without 

 sandstone, and therefore without any indication of coal ; the 

 Cranfield outcrop of blue carboniferous limestone extends to 

 both sides of Carlingford Harbour, and is extensively worked at 

 Carlingford for industrial purposes. The Carlingford limestone 

 determines the age of the Mourne granite, which has been 

 forced up from below through the silurian rocks and through 

 the limestone, both formations being indurated or baked by the 

 igneous action of the granite, which has converted the silurian 

 shales into banded hard rock of great beauty and capable of 

 high polish. The granite for the Albert Memorial, Hyde Park, 

 was selected from Castlewellan quarries, where there is an 

 inexhaustible supply awaiting the development of this branch of 

 Irish industries. The first formation of the mesozoic period 

 we find at the Antrim side of the harbour, forming the slopes 

 of Cave Hill, and indeed the foundation of the whole County 

 Antrim, in the form of a series of sandstones of various colours, 



