520 H. S. JEVONS, H. I. JENSEN, T. G. TAYLOR AND C. A. SUSSMILCH. 



leaves with almost the lustre of biotite and often nearly 

 3 cm. (1 inch) in diameter. Other bands or patches rich 

 in ilmenite have been found in other parts of the mass. 



Little can be said with certainty as to the distribution 

 of apatite, because it is almost impossible to estimate its 

 quantity with any approach to the truth by the Rosiwal 

 method unless unusually abundant. The impression gained 

 from all the slides made, however, is that there is a tendency 

 for apatite to be more abundant in the immediate neigh- 

 bourhood of segregation veins, whilst there is undoubtedly 

 a good deal of it in those veins themselves. Of the speci- 

 mens represented in the table, P comes from close beside 

 an aplitic vein, the Survey specimen (column V) probably 

 comes from near one, and column VI is the aplite, and all 

 have more apatite than specimen I ; but so has a specimen 

 of the pailio-essexite also (column II). 



The main features of the distribution of the minerals as 

 described above may be summarised thus: (1) the pailio- 

 essexite is richer in olivine and biotite than the main rock, 

 and its plagioclase is a little more acid; (2) a concentration 

 of felspar occurs in a layer extending horizontally probably 

 throughout the mass, and reaching downwards from a depth 

 of 4 or 5 metres below the junction with the shales to 17 

 metres, and always parallel with the junction; (3) the 

 irregular distribution of the iron ores, which tend, however, 

 to be much more abundant in the main rock than in the 

 pailio-essexite, especially than in the inner zone of the 

 latter (as represented by specimen C); and (4) the uniformity 

 in composition of the main rock below the segregation 

 veins so far down as it is anywhere visible. The principal 

 changes in composition have been found to be in a vertical 

 direction; as to whether there is any change horizontally 

 on a large scale in the mass as a whole, the exposures do 

 not warrant any certain conclusion. Probably the pallio- 



