180 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



until the sand was quite dry. It was then dark grey in colour. 

 When shaken out on to a sheet of paper it rapidly bleached 

 to the normal colour. It even bleached when kept in a 

 desiccator. 



When examined under a microscope the sand is seen to 

 contain black granules adhering to, and mixed among, the 

 grains, but the latter are not " coated." When it is treated 

 with dilute HC1 it bleaches at once and SH 2 is evolved. The 

 solution, when filtered, gives all the tests for iron. When the 

 sand is ignited strongly it also bleaches, but the iron is not 

 then so easily dissolved out, though it can be, of course. 



The blackening and subsequent bleaching are easily 

 imitated. Some very clean, white sand was ignited, cooled, 

 and then put into an evaporating basin and covered with a 

 0-5 % solution of ferrous sulphate. A little ammonium chloride 

 and ammonium hydrate were added, and SH 2 was bubbled 

 through the wet sand. The latter rapidly blackened. It was 

 then quickly washed in boiled-out water and put into a tall 

 glass tube with a little overlying water. In a few hours the 

 upper layer bleached and the result resembled that obtamed 

 from the naturally discoloured sand. Just the same effects 

 were produced when the mixture of clean sand and dilute 

 solution of ferrous sulphate was treated with ammonium 

 sulphide. The bleaching occurred in much the same way, but 

 the decolourised, upper layer was yellow because of the presence 

 of sulphur. Evidently, then, these littoral ; black sands 

 are the result of the formation of ferrous sulphide. Every- 

 where on this coast (and especially in the North Lonsdale 

 region) the sea- water in the interstices of the sand con tarns 

 soluble iron salts. Everywhere there are organisms (lugworms 

 and cockles, for mstances) which form excretal substances, 

 and in any case they die in the sand sometime or other. The 

 putrefactive process gives rise to SH 2 and some ammonia 

 salts, and then the trace of iron present in the water is precipi- 



