200 [Proc. B.N.F.C., 



while it is not unlikely that in the neighbourhood of the large 

 deposits of alkaline salts at Carrickfergus any minerals which 

 contain soda and potash in varying proportions would contain 

 them in relative abundance. It may be interesting here to 

 notice the figures given in the volume of the " Challenger " 

 Report referred to above for a reddened Glauconite in which 

 the silica, is exceptionally low, viz.: — 



Si0 2 Fe 2 3 Al 2 O s FeO OaO MgO K a O Na 2 H 2 Total 

 2774 39'93 13*02 [76 1-19 4*62 0*95 0*62 10-85 too*68 



To which the remark is attached " the high percentage of ferric 

 oxide and water points to a decomposition of this mineral, which 

 has been transformed into limonite as is often the case in 

 Glauconite from the geological strata with loss of silicic acid 

 and potash ; but this explanation can hardly be given for this 

 specimen which consists of casts from a coral sand." But no 

 alternative suggestion is made, and neither will the suggestion 

 hold in the case of our own Glauconite, for while the silica is 

 low the ferric oxide is not particularly high, nor is the water, 

 while the potash is seemingly higher than usual. Moreover, 

 the casts are green and show no signs of decomposition at all, 

 which would certainly be the case if this decomposition into 

 limonite were taking place. Professor Cole has suggested that 

 possibly in the course of ages silica has actually been abstracted 

 in solution ; but in this case, since the silica must have been 

 in combination when present in the mineral, the grains should 

 show some signs of the decomposition which must have taken 

 place, and no such signs are visible. The only conclusion to be 

 arrived at in our present information would seem to be that the 

 Glauconite from Woodburn is of the same composition as when 

 originally formed, but why in this spot it should contain an 

 unusually small percentage of silica is beyond my power to 

 suggest. 



I trust I may have a further opportunity of examining speci- 

 mens of Glauconite from this locality with a view to determining 

 the constancy or otherwise in composition of this deposit. 



