3o6 The Irish Naturalist. [Nov., 



GEOLOGY. 



Post-Tertiary beds at Ballyhalbert, Co. Down. 



Seven or eight years ago, when I was working at the marine post- 

 glacial deposits of the north-east, Mr. W. Swanston told me of having 

 observed many years before a bed apparently of the " estuarine clays," 

 so extensively developed at Belfast, on the outer shore of the Ards 

 peninsula, between Millisle and Ballywalter, and I searched the shore 

 between those two places for this bed without success. Last September, 

 when cycling along the coast of the Ards, I saw on the shore between 

 Ballywalter and Ballyhalbert a deposit which, from Mr. Swanston's 

 description, I at once recognised as that which he had seen ; but I could 

 devote only a few minutes to its examination. The shore here is stou}'. 

 A slope of large pebbles occupies the upper portion of the shore to about 

 half-tide level ; below that level the boulder-strewn shore stretches with 

 a very slight slope to low-water mark. The highest zone of the post- 

 glacial beds here exposed consists of a few inches of bluish clay, running 

 in under the steep shingle-beach some feet below high-water mark. 

 The clay contains Zostera, but I saw no shells ; it resembled in every 

 respect the Lower or Scrobicularia clay which occurs at so many places in 

 the north-east. Below this zone was a bed about six inches thick of 

 solid peat. It contained numerous stumps of trees with roots spreading 

 horizontally in all directions, and trunks and branches of trees. I 

 measured one trunk twenty-seven feet in length. The stumps appeared 

 to belong to the Scotch Fir, though I found no cones. The peat is only 

 seen close to the edge of the shingle-beach. Lower down it has been 

 worn off the top of the underlying beds, which consist of very fine pink 

 and grey laminated clays, three feet at least in thickness. Their base is 

 not seen. They cover an area of perhaps an acre along the beach, and 

 it is their horizontal beds that attract the eye from the road. These 

 clays contained no fossils so far as I could see ; and they looked identical 

 with the clays which underlie the salt-marsh behind Killough in Co. 

 Down, and out of which bricks are now made. The exact spot where 

 these interesting beds may be seen is one and a quarter mile north of 

 Ballyhalbert, and just south of the spot marked " Rodden's Port" on 

 the one-inch O.S. map. 



R. L1.0YD Praeger. 



