ASSOCIATED IGNEOUS ROCKS OE THE AYRSHIRE COAST. 771 



ruginous microliths. There is in the slide a grain or two of a dark 

 brown mineral, possibly picotite. I have not the slightest doubt 

 that this is an altered olivine- ens ta tit e rock. 



The following is Mr. Houghton's analysis of the " serpentine freed 

 from enstatite;" and I reprint, in a parallel column, that of the 

 Cadgwith serpentine by Mr. Hudleston (loc. cit. p. 925). A compa- 

 rison of these will show haw closely they correspond. 



Balharuie. Cadgwith. 

 (Dried at 100° C.) (Dried at 100° 0.) 



Water 14-08 12-35 



Iron sulphide trace 0-41 



Silica 38-29 38-50 



Alumina* 3-95 1-02 



Iron sesquioxide 2-53 4*66 



Iron protoxide 4-04 3-31 



Lime 057 1-97 



Magnesia 35-55 36-40 



Manganese oxide trace 



Nickel oxide 0-15 0-59 



Residue 1-37 



99-16- 100-58 



In the quarry is seen an irregular vein of a greenish mineral, not 

 exceeding about 4 inches thick. Mr. Houghton reports as follows : 

 — " Amorphous, hardness about 3 ; S.G. 2-87. It is fusible at the 

 blowpipe with some difficulty. It is entirely decomposed by hydro- 

 chloric acid, leaving the silica in a pulverulent condition. 



" Its composition is as follows : — 



H 2 9-52 



C0 2 traces. 



Si0 2 33-13 



A1 2 3 17-63 



Fe 2 3 0-30 



FeO 6-57 



MnO traces. 



CaO 10-31 



MgO 21-26 



98-72 



* The percentage of alumina is rather large, but there is certainly no felspar 

 present or any other mineral akin to it. Perhaps the difference between the 

 two rocks in this respect may be thus explained : the bronzite in the Balhamie 

 rock is more altered than in that from Cadgwith, and so a less quantity may 

 have been separated from the serpentine by the method employed. Mr. Hud- 

 leston found that there was a fair amount of alumina present in the Cadgwith 

 bronzite, and so there probably is in that of Balhamie. Hence the amount of 

 alumina present in the serpentine proper is probably rather less than appears in 

 the analysis. 



3f2 



