TWO NEWLY-DISCOVERED WHIN-DYKES 337 



for the sum, A] 2 03+Fe. 2 3 =34 , 93 per cent, as against 35*23 

 calculated. 



Again, taking the specific gravity of albite as 2'6o5, that of 

 anorthite as 2*765, the value calculated for the mixture of the 

 two in the above proportions is 2752; this agrees with the 

 value found for the Hartley inclusion, namely, 2750. 



The microscopic examination of the felspar would be of 

 considerable interest in view of its identity in composition 

 with the Crookdene felspar and the petrological peculiarities 

 of the latter {op. cit. p. 8). Owing, however, to its brittleness 

 and the small amount at disposal, it was found impossible to 

 make a section of the mineral thin enough for satisfactory 

 examination. 



4. Weathering of the Whin. It is unfortunate that no rock 

 fresh enough for analysis is obtainable from the Hartley Dyke. 

 There is, however, every reason to expect that the com- 

 position of the fresh rock will correspond closely with that of 

 the other anorthite-bearing dykes in the district, especially the 

 Crookdene and Collywell dykes, which are almost identical in 

 composition {op. cit. p. 3). The weathering of the Crookdene 

 Dyke has been worked out in some detail {op. cit. p. 7), and it 

 has been shown that the augite, which is replaced by calcite, 

 is rich in magnesium and has a silica-content almost equal to 

 that of the original basalt ; further, that the felspars, which 

 resist weathering to a much greater extent than the augite, 

 are allied to labradorite. 



The results of a partial analysis of the highly weathered 

 whin from the lower exposure of the Hartley Dyke are given 

 in Table C, No. I., and also, for comparison, the corresponding 

 values for the weathered Crookdene rock (No. II.). 



Table C. Partial analyses of weathered rock from Hartley Dyke (I.) 



and Crookdene Dyke (II.) Total iron reckoned as Fe2C>3. 



I. II. 



38-06 



24'3i 



20-42 



0-87 



10-37 



Si0 2 



33-37 



Oxides of Fe, Al, Ti 



25-10 



CaO 



21-63 



MgO 



in 



C0 2 



13-66 



