ON THE MARINE ZOOLOGY OF THE IRISH SEA. 333 



kindly sent the following notes in regard to it :— ' The microscopic ex- 

 amination shows that it is practically a fine-grained grit made up of the 

 usual constituents of fragmental rocks cemented together, the cement 

 being in greater quantity than the grains. These grains are chiefly chips 

 of quartz, but I have also seen microcline, orthoclase felspar, plagioclase 

 felspar, brown mica, a tew grains of glauconite, and green and brown 

 pseudomorphs, probably after grains of some ferro-magnesian mineral 

 like augite, hornblende, or even possibly olivine— which it is impossible 

 now to° say, but I think most probably hornblende. There are one or 

 two opaque grains, and several clear grains containing a good deal of 

 minute magnetite. The grains vary in size within small limits ; the 

 largest I have measured is 0-02 inch and the smallest 002 inch, but the 

 average size would be about 0-004-0-005 inch in longest diameter. They 

 are therefore minute grains, and, as might be expected, extremely angular, 

 not one in a hundred showing rounded outlines. They are chiefly such 

 o-rains as would come from the denudation of granitic rocks or sediments 

 derived from them. 



' The cement is carbonate of lime, with a small impurity of carbonate of 

 iron, present chiefly in certain layers, but not there in any considerable 

 quantity. The cement is clearly crystalline in immediate contact with the 

 grains, and also where lining cracks and cavities. Elsewhere it is more 

 opaque, and less conspicuously crystalline. The section cuts across 

 numerous shell fragments and a few polyzoa, and where there are any 

 hollow structures, as in the inside of lamellibranchs or gastropods, they 

 are filled up with a substance indistinguishable from the bulk of the 

 concretion. 



' The specimen shows no particular reason for the local deposit^ of 

 cement, and the other constituents are doubtless the ordinary materials 

 of the sea-bed. I cannot find any evidence that the cementing is due to 

 any organic agency, and the thoro'.ighly well-developed crystals of car- 

 bonate of lime quite agree with this. It may be that the Carboniferous 

 limestone crops out on the sea-bottom under the deposit, and, if so, there 

 would very likely be submarine springs laden with carbonate of lime 

 which might be precipitated there under less pressure or local loss of 

 carbonic acid. It may be added that Mr. Clement Reid could not see in 

 the specimen any identifiable shells of other than recent age.' 



Another possible explanation is that the smaller calcareous particles 

 on the bottom have been dissolved in the sea-water and then re-deposited 

 so as to cement together the larger shells and the sand grains. 



As was mentioned earlier in the report, sample bags of all the more 

 important submarine deposits we have come upon have been sent, at 

 Sir Archibald Geikie's request, to the Museum of the Geological Survey 

 in Jermyn Street. They are being examined there by Mr. Clement 

 Reid, F.'G.S., who writes the following preliminary note in regard to 

 them : — 



' On comparing these samples with British deposits of Tertiary date 

 one finds a marked diflference in lithological character. Dredgings from 

 the Irish Sea, and also from the North Sea, are characterised by a 

 much coarser and more gravelly texture than one would expect at such 

 <iepths— coarser, in fact, than one finds in Pliocene deposits, yielding a 

 .similar fauna, indicating similar or even smaller depths. A glance at 

 these dredgings shows the reason of this, for they are largely composed 

 of unworn or little-worn fragments of rock, often entirely encrusted by 



