I904- GouGH. — Iro7i Ore in Lough Nea^h. 89 



ing the gradation from such as I have just described to those 

 where the nucleus can onh^ be detected b}' grinding down a 

 section and examining it under the microscope. 



Selecting some of those which appeared to consist chiefly 

 of ore, I found the specific gravit\', taken with a Jol3''s balance, 

 to be 2-53. These were crushed, dried at 100° C, weighed 

 and treated as previous specimen, the percentage of iron being 

 36-93. Calculated as limonite, the percentage is 61 "66, the per- 

 centage of the insoluble residue being 36-51, giving a total of 

 98-17 per cent. The remainder consists apparently of a small 

 quantity of magnesium carbonate ; no manganese, phosphoric 

 acid, or calcium being found. The COo in the specimens 

 seems to vary greatly, some giving little or no effervescence 

 with acid, others a fair amount, but none very much. 



From my examination, it appears to me that the ore is being 

 formed chiefly from the decomposion of the magnetite in the 

 basalt in and around the lough. As suggested by Prof. 

 Cole, in a note attached to Mr. Welch's letter, I have examined 

 the gelatinous residue remaining after solution of the iron in 

 dilute HCl, but have found no trace of cellular structure 

 either in the form of Algae or Diatoiiiacese. I believe that the 

 altered iron in the fragments of basalt acts as a segregation 

 centre on which the limonite is deposited from the iron in 

 solution in the lough, on the smaller particles, with a concentric 

 structure. In the section of the " cinder " there seems to be 

 continuity between the iron in the basalt and the ore incrust- 

 iug it. Whether the Tertiary iron ores were formed in the 

 same way I cannot sa}^ but I intend to section some 

 specimens of pisolitic ore in the hope of finding a similar 

 nucleus of basalt. 



In conclusion, it is interesting to note that the pisolitic ore 

 now forming is practically pure limonite, while that incrust- 

 ing the " cinders " is an impure variet}^ having the usual com- 

 position of the bog ores. 



Queen's College, Belfast. 



