TWO NEWLY-DISCOVERED WHIN-DYKES 335 



blocks are usually found to have a core of bluish rock re- 

 sembling ordinary basalt, though lighter in colour. The 

 freshest rock obtainable, however, is very much decomposed, 

 having a specific gravity of 2-658 and containing io # 53 per 

 cent, of carbon dioxide — equivalent to 23-9 per cent, of 

 calcium carbonate. 



Under the microscope, the structure of the basalt is plainly 

 discernible. The rock is much finer grained than most of 

 the local dykes, and the amygdaloids, which are abundant, 

 are also small. In the best sections the felspars are fresh ; in 

 the highly weathered rock they show some signs of decom- 

 position. The augite is completely replaced by calcite, and 

 great obscurity results from the dissemination of much 

 secondary oxide of iron. No porphyritic felspars occurred in 

 eight sections of the rock examined. 



The whin does not appear to have altered the rocks in 

 contact with it to any appreciable extent, except in the case of 

 the coal, already mentioned, which is converted into a clean, 

 prismatic coke. A proximate analysis of this, kindly carried 

 out by Mr. L. Hawkes, B.Sc, gave the result : 



Volatile Matter 19.83 



Fixed Carbon 58-88 



Ash 21-20 



The analysis shows the high ash-content and low volatile 

 matter common to cinder-coals. 



3. The Felspar Inclusions. Although, as stated above, no 

 porphyritic felspars occur in any of the slides examined micro- 

 scopically, yet several small felspar aggregates were found in 

 the whin of the upper exposure, the largest being about 

 i-cubic inch in volume. The felspar is, in the main, extra- 

 ordinarily fresh, with well developed cleavage, and the corners 

 of the aggregates are quite sharp. It was prepared for 

 analysis by crushing and sifting, treatment of the coarse 

 powder with very dilute acid and separation by means of 

 Sonstadt solution. Selected fragments of the felspars thus 



F 



