14 FISHES AND FISHERIES OF THE IRISH SEA. 
lump in the Biological Station at Port 
Erin, and we have presented another 
piece to the Jermyn Street Museum in 
London. Mr. W. W. Watts, F.G.S., 
has made a careful examination by thin 
sections of the latter specimen, and he 
has kindly sent us the following notes in 
regard to it :—‘*‘The microscopic exami- 
nation shows that it is practically a fine 
grained grit made up of the usual con- 
stituents 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 few 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 quite opaque grains, and_ several 
clear grains containing a good deal of 
EiGeis: minute magnetite. The grains vary in 
size within small limits, the,largest I have measured is 0 02 inch, and the smallest 0.002 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 grains 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 is 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 thoroughly well 
developed crystals of carbonate 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,” 
