Vol. 54.] CHLOKITOED IN KINCAEDINESHIBE. 155 



in getting rid of this marginal material, and a considerable quantity 

 of nearly pure chloritoid has to be taken, in order to prepare a 

 small sample pure enough to give a true analysis. Fortunately 

 the presence of white mica as a source of impurity can be instantly 

 detected by the alkalies shown in the analysis. Neitlier potash 

 nor soda occurs in any of the chloritoids, and so long as either 

 was present in appreciable quantity the analysis could not give 

 the true composition of the mineral. The four analyses showed 

 the steady decrease of this source of impurity. I regret to say 

 that the record of the first has not been kept, as it was obviously 

 made with impure material. Mr. Hutchings has kindly supplied 

 the account of the second. The lime present in Nos. II. and III, 

 is probably contained in the white-spot material, which was not 

 separated entirely except from the last sample analysed. 



SiO^ 



AiA 



FeO 



Fe,0, 



I. 



II. 



31-40 

 37-38 

 18-81 



2-80 

 3-05 

 0-38 

 0-65 

 5-45 



III. 



30-00 



3610 



18-57 



5-03 



2-00 



302 



0-50 



5-00 



IV. 



2600 



4005 



19-50 



5 05 



CaO 



MgO 



K3O 





2-88 



Na^O 



H^O 



::::::;:: ji-^ 



Trace. 

 600 



99-92 100-22 9948 



G. B.— February 4th, 1898.] 



Discussion. 



Sir Archibald Geikie said that, although he rose in obedience 

 to the President's call, he did not feel that he had sufficient personal 

 acquaintance with the subject of the paper to warrant him in 

 offering any criticism. He was glad of the opportunity, however, 

 of welcoming a paper of this kind in the meeting-room of the 

 Geological Society. Those whose memories carried them back 

 30 or 40 years would remember how completely the field-geologists 

 of this country had then thrown over the practical aids of chemistry 

 and petrography. Such a contribution as that to which the 

 Society had just listened it would have been almost impossible 

 for any of those men to produce, admirable observers as they were. 

 Mr. Barrow had shown that, besides being an excellent surveyor in 

 the field, he was also a skilled chemist and trained petrographer. 

 He was engaged in working out the structure of some of the most 

 difficult country in the Central Highlands, and devoted himself also 

 with the most praiseworthy enthusiasm to the study of the chemical 

 and mineralogical characters of the rocks which he encountered. 

 His work had thus a special value, for it united a grasp of broad 

 questions of tectonic geology with a laborious devotion to the 

 investigation of the minutest features in the composition and 

 internal structure of the rocks. 



