566 



Proceedings of the Royal Irish Academy. 



Allowing for these it will be observed that the compositioii corresponds 

 roughly with that of a "piom'ce^^ or obsidian. In order to determine 

 how far this estimate ndght be coiTect, two specimens of calp were 

 taken from Finglas qnarry ; the one a relatively pure limestone (I^o. 

 74), the other a calp shale (I^o. 75). Both were pulverized and 

 treated with HCl until the lime was removed as far as possible. The 

 residues were then submitted to ^MJr. "Warren who sent in the following 

 Eeports of the analyses : — 





(Xo. 74). 

 Percentage. 



(Xo. 75). 

 Percentage 



SiO,, . 



78-66, 



75-02 



AL63, . 



10-80, 



12-57 



Fe^Oa, . 



— 



— 



FeO, . 



5-25, 



4-19 



3InO, . 



— 



trace 



CaO, . 



0-71, 



1-14 



MgO, . . 



0-93, 



1-72 



Isa.O, . 



0-32, 



1-01 



K,0, . 



trace. 



0-26 



P2O5, . 



trace, 



— 



S, , . 



3-21, 



4-02 



Moisture and 

 organic matter, ) 



0-41 



O'll 



V ^ J, J • 





100-29 



100-04 



Nos. 74, 75. — " Received in the form of a black, ground powder, 

 containing small quantities of pyrites, which have been calculated, 

 as ehown iu the above analyses." 



" Both samples were carefully examined for rare metals of the I., 

 II., III. and lY. groups, but only the very minutest trace of TiO, 

 was found in Xo. 75." 



Parts of these same residues were treated with nitric acid in order 

 to completely remove the pyrites present, which owing to the fineness 

 of its state of division could not be perfectly separated by panning. 



The densities of these final residues thus freed from pyrites were 

 found to be : — 



Xo. 74 (calp limestone residue) D = 2-124. 

 iN'o. 75 (calp shale residue) D = 2-074. 



These densities are characteristic of pumices, while the composi- 



