124 W. M. Hufehings— Rocks of Great Whin Sill. 



a good deal of recrystallized silica. B is a rock practically free 



from minerals other than calcite — only a very few garnets and 

 a little quartz : — 



A. B. 



99-67 



100-87 



A portion of B -was dissolved slowly in dilute cold hydrochloric 

 acid, the residue filtered and dried, and its alkalies separately 

 determined. It gave : — 



Potash 

 Soda 



0-35 per cent. 

 0-78 



Another limestone, completely recrystallized, and showing grains 

 and small indeterminable crystals of foreign matter, gave : — 



Potash 

 Soda 



0-26 per cent. 

 0-81 



This rock, dissolved in dilute acid, gave a residue which, after 

 filtration and ignition, was 6 per cent, of the original material, and 

 contained : — 



Potash 

 Soda 



0*58 per cent. 

 6-30 



All the above show large excess of soda, but amongst the lime- 

 stones, also, we find contradictory results. Thus, one altered bed 

 containing augites, etc., gives : — 



Potash 

 Soda 



2 "55 per cent. 

 0-62 



Another hand-specimen shows sugary white limestone, together 

 witli a layer of brown hornfelsy rock, due to impurer material. 

 The alkali-contents are : — 



Potash 

 Soda 



White Limestone. 

 0"30 per cent. 

 0-07 



Brown Layer. 

 5-79 per cent. 

 1-40 



At my request, Mr. Garwood collected a series of specimens 

 representing the succession of beds downward from the Whin Sill 

 to the basement conglomerate, at Falcon Glints, in Upper Teesdale ; 

 as I thought it would be of considerable interest to make alkali- 

 determinations in them, and at the same time examine them micro- 

 scopically and note the nature and intensity of the alterations. 

 The particulars of the section at this point, as given to mo by 

 Mr, Garwood, are as follows : — 



