MAEINE BIOLOGICAL STATION AT PORT ERIN. 191 



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 there- 

 fore 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 de- 

 nudation 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 Eeid could not see in the specimen any identifi- 

 able shells of other than recent age." 



Manx Natural History Society. 

 The Isle of Man Natural History and Antiquarian 

 Society arranged to hold one of their Summer meetings 



