154 Scientific Proceedings, Royal Dublin Society. 



The laterites between the dolerite flows are generally of a red, 

 or reddish brown, colour and very tough ; it is invariably amyg- 

 daloidal, the cells containing zeolites and aragonite. The laterite 

 partings between the lower beds of dolerite are usually softer or 

 more decomposed than those between the upper beds, and very 

 often graduate into thick ochre and bole beds ; this is not so 

 common in the upper dolerites, biit in every case which has come 

 under my notice the iron ore measures alone excepted, the 

 laterites are very vesicular and contain large quantities of 

 zeolites. I have also frequently observed manganese oxide in 

 fche cells. 



From the papers and memoirs on the laterites and associated 

 iron ores to which I have had access, it would appear that they 

 are supposed to be accumulations due to the disintegration of 

 trappean rocks during periods of successive volcanic outbursts ; 

 for such a theory I do not, however, see sufficient evidence. The 

 thin ferruginous beds of bole between most of the large flows 

 may doubtless be formed from the disintegration of the scoria or 

 .mrface of the flows ; but the materials forming the thick beds 

 such as the iron ore measures, could scarcely have had such an 

 origin. Their thickness, structure, and other characters suggest 

 that possibly they are eruptions of ferruginous mud, ejected at 

 intervals between the basaltic flows by volcanic agencies, or 

 perhaps eruptions of ferruginous dolerites and tufls which subse- 

 quently decomposed in situ. The beds of aluminous ore seem 

 to be contemporaneous with the accumulation of the associated 

 beds, and in all probability are a sedimentary deposit, but the 

 pisolitic ores have characters which would appear to refer their 

 origin to some other cause. 



The iron ore measures of Antrim vary from ten to seventy feet 

 in thickness ; in the Glenarift' mines they do not exceed sixty 

 feet ; they and the associated rocks give the following section :— 



Feet, , 682 



