234 The Irish Natu7alist. November, 



The deposit seems distinctl}- connected with the esker-stage 

 of glacial melting, and no doubt represents the track of a side 

 flow, here locally dammed up and checked, which descended 

 from the slope on which the well-known csker of Balrothery 

 stands. We have here preserved for us, laid down in some 

 chance and probably narrow backwater, a part of the material 

 washed out from the boulder-clay during a late glacial stage, 

 while the esker and the local flood-gravels represent the 

 coarser residue. 



Seeing how readily the limestone blocks in the upper layers 

 of exposed boulder-clays yield up their calcium carbonate and 

 leave only clayej^ residues, it is somewhat surprising to find 

 that the very fine clay of Templeogue is still highly calcareous. 

 The whole material is of course much finer than the two- 

 millimetre grade which is selected as the upward limit of the 

 "fine earth" of ordinary soils. Mr. W. D. Haigh, a.r.c.sc.i., 

 has kindly determined the calcium carbonate present, in the 

 laboratory of the Geological Survey, and finds it as high as 

 24*3 per cent. When sifted through the finest practicable 

 wire sieve, with meshes -02 mm. in diameter, a very few grains 

 of quartz sand remain upon the sieve. I have found no fora- 

 minifera or other organisms. The great mass of the material 

 washes through, and this, when examined microscopicall}', 

 appears to consist of very fine mud and sand. When treated 

 with hydrochloric acid, considerably more than 25 per cent, of 

 this fine matter is at once dissolved with effervescence, showing 

 that the mud consists largely of comminuted limestone. Sul- 

 phuretted hydrogen is evolved, doubtless from iron pyrites. 

 The undissolved residue seems equall}" fine, with the exception 

 of a few coarser sand-grains, which now assume prominence, 

 and one or two minute prisms of zircon. From this we may 

 suspect that, when our boulder-clays near Dublin are examined 

 from a chemical point of view, a large part of their " mud " may 

 prove to consist of undestroyed detrital limestone. Mr. Kilroe 

 informs me that such clays effervesce freely when placed in 

 acid. 



Geological Survey Office, Dubliu. 



