534 



J. NOLAN ON THE OLD BED SANDSTONE 



3. Not recognized. 



Upper Old Eed Sand-^l 

 stone (Kiltorcan 



Coarse yellow sandstone "* 

 and pebble-beds, passing 

 downwards into pink, 

 reddish-brown, and pur- 

 ple sandstones and con- 

 glomerates full of white 

 and pink quartz pebbles. ) 



Old Eed Sandstone of )■ Upper Old Eed Sand- 



the Galtees, Water- 

 ford, &c. " Old Eed 

 Sandstone proper " 

 (Jukes). 



; 



UNCONPORMABILITY. 



UNCONFORMABILITY, 



1. Parple micaceous sand- ^ 

 stones and coarse con- ', 



glomerates, with felstone i Dingle beds and Glen- 

 (porphyrite) pebbles and | gariff grits, 

 contemporaneous volca- 

 nic rocks (Fintona beds). ) 



stone. 



UNCONFORMABILITY. 



Lower 



stone. 



Old Eed Sand- 



Should the Old Bed Sandstone he considered a distinct formation 

 from the Carboniferous? — As this latter formation appears to be 

 everywhere conformable to the former, we may be inclined to regard 

 the Old Eed Sandstone rather as the base of the Carboniferous 

 system than as a separate and distinct one ; yet the circumstances 

 under which they were formed must have been very different — the 

 one being a marine, the other a freshwater deposit. The great lakes 

 in which the Old Eed Sandstone seems to have been formed pro- 

 bably gave place gradually to lagoons, and ultimately became 

 merged in the sea wherein the Carboniferous strata were subse- 

 quently accumulated. The direction of the depression seems to 

 have been northwards, for the greatest masses of Old Eed Sandstone 

 occur in the south, principally in the counties of Cork and Water- 

 ford; they are also largely spread around the Silurian rocks com- 

 posing the hills that extend semicircularly from the vicinity of 

 Lough Derg to the Slieve-Bloom range. Little of it is seen on the 

 east, the older rocks there forming low ground ; to the west and 

 north masses of considerable extent, though of far inferior area to 

 those in the south, appear to have fringed the ancient shores of the 

 metamorphic and Silurian rocks that make up the highlands in these 

 districts ; while in the central parts little occurs, except where, 

 through faults or subsequent folding and undulation of the strata, 

 portions reappear in the midst of the great limestone plain. 



The persistence of a very remarkable lithological character is 

 also well worthy of observation, for in few places is the rock com- 

 posed of any local debris, but, on the contrary, is generally totally 

 different, being derived from some source apparently unknown — a 

 fact which, taken in connexion with the wide area over which it is 

 found, is suggestive of the original great extent of the deposit. 

 That this merely represents the area of the ancient lakes is by 

 no means probable, but rather the greater part of the floor of the 

 Carboniferous sea.. As depression continued, limestones would be 

 formed in the deeper waters, while near the land sandstones, 

 shales, &c. would be deposited, in this way giving rise to the great 



