366 ScientiflG Proceedings, Royal Dublin Society. 



It is of course not a normal serpentine insomuch as the propor- 

 tions are not those of the mineral, but in every respect answers 

 fairly to the character of serpentine roch. At any rate the term 

 aluminous magnetitic serpentine would be a correct name for it* 



In no case have I obtained a specimen of it without magnetite, 

 even the compact specimens contain a little of this, and it occurs 

 in all quantities from 2 per cent, up to 15 per cent, nearly. I 

 have not tested specimens containing less or more, but, I have no 

 doubt they may exist. . . . , 



If the rock is finely powdered and a magnet passed through it 

 the magnetite forms a brush on the poles ; a quantity of it can 

 be taken out thus. 



I applied this method for the determination of the per-centage, 

 but I find that Bischof, who has a very aggravating way of antici- 

 pating geological chemists, used the same method for the extraction 

 of the magnetite from the serpentine of the Heidelberg. He 

 mentions that as much as 13"6 per cent, was extracted in this way, 

 but that the actual proportion must have been smaller as it would 

 be difficult to eliminate it completely from the rock. 



The Sligo rock therefore contains the highest recorded per- 

 centage. 



In order to be certain that the magnetite was entirely eliminated 

 I subjected the powder to frequent levigation and elutriation, 

 sifting frequently with the maguetj.so that I do not believe that 

 OlO per cent, of rock remained attached to the mineral when 

 finally weighed. 



In conclusion I would briefly remark on the bearing of the 

 presence of this mineral on the origin of this serpentine rock. 



I need hardly refer to the fact that serpentine is never found 

 unassociated with metamorphic or igneous rocks. Yet there 

 are some who hold that serpentine may be deposited amongst 

 sedimentary rocks as a wholly aqueous deposit. Id will be in 

 memory of those present that Dr. Sterry Hunt in a very able 

 paper read at the last Dublin meeting of the British Association 

 strongly upheld this view. 



Now the Sligo serpentine would at first sight appear to agree 

 with this view. It is most clearly a stratified rock, well and very 

 regularly bedded, and perfectly well defined with regard to the 



* It is possible indeed that the rock should be called eklogite serpentine if it could be a 

 product of alteration of augitic rocks. This however is improbable. 



