126 W. M. Eutchings—Rochs of Great Whin Sill. 



crystalline. But there are many " spots " in the sections, in 

 which, among a good deal of indeterminable matter, some chlorite, 

 etc., are a good many small bits and prismatic crystals of augite. 

 Some augite occurs also outside these spots, but not much. The 

 alkalies are : — 



Potash. ... ... ... ... ... ... 2-55 per cent. 



Soda 0-62 



No. 4. A main mass of fine-grained shale, in which are bedded 

 good large quartz fragments, with numerous flakes of clastic mica, 

 and a good many grains of calcite. The coarser constituents are 

 not altered, but the finer portion has been completely regenerated, 

 giving rise to a small-grained dim sort of mosaic, with a little new 

 mica, and showing here and there larger patches of this and of 

 chlorite. This rock contains : — 



Potash ... ... ... ... ... ... 3"55 per cent. 



Soda 2-76 ,, 



No. 7. This limestone is very much recrystallized, but does not 

 show any distinct new minerals, being only slightly impure : — 



Potash ... ... 0-26 percent. 



Soda 0-81 ,, 



No. 8. A sandstone converted into a quartzite. There was very 

 little interstitial matter, which is now much altered, but details 

 cannot be made out : — 



Potash 0'23 percent. 



Soda 1-12 ,, 



No. 9. This is the bed described as " an interesting contact- 

 rock," the main characteristics of which were recapitulated above, 

 so that no description need be given here. It was pointed out that 

 the bed varies more or less in composition in different parts, being 

 more or less quartzy, etc. As since I first described it I have made 

 some more alkali-determinations on various specimens, it may be 

 worth while to add them here : — 



per cent, per cent. per cent, per cent, per cent. 



Potash 1-01 ... 0-47 ... 1-60 ... 2-71 ... 070 



Soda 1-92 ... 1-10 1-31 ... 1-35 ... 1-33 



The last is from a sample representing a large number of the 

 "nodules," which were carefully detached from the rock. 



We do not know how far from the contact the metamorphisra 

 caused by the Whin Sill was capable of extending, but we have here 

 an instance of very great alteration at over 80 feet distance, and 

 may safely say that the action would have continued much further. 

 From published observations on the subject, it does not seem usual 

 for the contact-zone of basic dykes or sheets to be as extensive 

 as this. 



The interpretation of the chemical determinations above given 

 does not seem to be an easy or a satisfactory business, owing to 

 their contradictory nature. Many of them show an undoubted 

 access of soda, at least — that conclusion seems to be unavoidable, 



