﻿part 2] 



LUBGECOMBE MILL LAMPEOPHYBE. 



31 



possible that some of the hiotite on the margin has been formed in 

 consequence of assimilation. 



Inclusion II. — In this case the bulk of the inclusion consists of 

 a transparent brown crystal. The mineral has a high refractive 

 index (almost exactly 1* 74), shows two fairly well-defined cleavages 

 inclined at about 80°, a pleochroism from pale to darker brown, 

 and polarization in first-order yellow. The fast direction of 

 vibration is also that of minimum absorption. The almost straight 

 isogyre sweeps across the field in such a way as never to coincide 

 with a cross-wire, and this fact, as pointed out by Dr. J. W. Evans, 1 

 may be taken as indicating the biaxial character of the mineral, 

 which is identified as staurolite. Associated with it, and showing 

 a strong tendency to occur along the cleavages, is a quantity of 

 dark, almost opaque material which is probably magnetite. 



Embedded in the staurolite are several crystals of corundum, of 

 the type already described. Also embedded in the staurolite are 

 a few small crystals which have a rich green colour and a high 

 refractive index. These are isotropic between crossed nieols, and 

 are considered to be green spinel. 



Surrounding the staurolite is a fairly definite zone of fine-grained 

 colourless material polarizing in first-order colours. In this zone 

 are several crystals of biotite which seem to have a curious influence 

 on the black matter of the staurolite. This black material 

 also tends to occur surrounding the staurolite as a band in close 

 contact with it ; and this, when coming on the inner side of the 

 biotite, bends outwards so as to form a lining to a channel (PI. IX, 

 fig. 2) communicating between the two minerals, staurolite and 

 biotite. It would appear that this biotite has been developed in 

 consequence of a process of, assimilation of material from the 

 xenolith. 



Inclusion III. — The minerals making up this inclusion are 

 staurolite, corundum, colourless mica, and magnetite. The chief 

 peculiarity is that the whole is surrounded by biotite ; and it is 

 suggested that this mineral has been formed in the same way as 

 that associated with Inclusion II, that is, in consequence of the 

 assimilation of a portion of the foreign material. 



It is worthy of notice that the emery in the norite of the 

 Cortlandt Series is often surrounded by an abundance of biotite. 3 

 The phenomena of the Cortlandt Series, however, are on a much 

 bigger scale, and the inclusions described by Prof. A. Lacroix 3 

 seem to supply cases which are more nearly of the same order of 

 magnitude. 



There can be little doubt that these occurrences of corundum, 

 staurolite, green spinel, and associated minerals have been developed 



1 Joum. Quekett Micro. Club, vol. xu (1915) p. 618. 



2 G-. S. Rogers, ' Geology of the Cortlandt Series & its Emery Deposits ' 

 Ann. K Y. Acad. Sci. vol. xxi (1911) p. 77. 



3 ' Les Enclaves des Roches Volcaniques ' Ann. Acad. Macon, vol. x (1893). 



