THE METAMORPHIC ROCKS OF ADELIK LAND. STILL WELL. 161 



extending as a circular bight into the side of a hypersthene crystal (Plate IV., fig. 3), 

 there can be little doubt that the hypersthene has taken part in the formation of this 

 aggregate. 



The radial arrangement of the small biotite crystals is very noteworthy, and it is 

 so constantly associated with the intergrowth of felspars (Plates IV., fig. 5 ; V., fig. 4). 

 The intergrowth has normally a fan-shaped arrangement and frequently branches from 

 a biotite flake (Plate XVI., fig. 6), and there can be little doubt that there is a genetic 

 connection. The biotite rosettes often surround an ilmenite nucleus, and, while there 

 is a similarity with an ordinary zone, significance must be attached to the different 

 structure. Though it is difficult to offer definite proof, the whole arrangement suggests 

 the reversal of the biotite-garnet reaction described in No. 947. If we imagine first 

 the formation of the garnet zone around ilmenite as in No. 947 (Plate V., figs. 5 and 6), 

 and then a reversal of the metamorphic conditions to those on the biotite side of the 

 reaction, whereby the garnet disappears and the biotite reappears, we might get the 

 rosetted biotite zones. Such hypothesis provides an intelligible account of the connection 

 between the biotite sprays and the associated myrmikoidal felspar. The evidence of 

 this reversal includes the presence of the garnet fragments in the quartz-biotite zone 

 (Plate IV., fig. 3) which lies between a hypersthene crystal and a large ilmenite surrounded 

 by biotite rosettes. Secondly, a break in the garnet zone around biotite (Plate IV., 

 fig. 3) is found, and the break is marked by a biotite spray which opens out into a 

 myrmikoidal fan which is only visible between crossed nicols, and, therefore, not seen 

 in the photograph. The sprays are also poorly developed on the outside of this garnet 

 rim. The incompleteness of the garnet rim around ilmenite and biotite (Plate VI., 

 fig. 1) may be explained in the same manner. 



The felspar in the slide consists of orthoclase, plagioclase (oligoclase andesine), and 

 the myrmikoidal intergrowths. Blebs of quartz may be set in the plagioclase which may 

 be rimmed with the intergrowths (Plate IV., fig. 5). A case has been noticed where the 

 plagioclase is separated from orthoclase, containing abundant minute fusiform inclusions 

 with higher refractive index, by a zone of intergrowtha. Large crystals of quartz are 

 irregularly distributed through the slide, in addition to the fine quartz in the biotite 

 aggregates and in the felspar. Pyrite and zircon are accessory. 



No. 785 (4). No. 785 (4) is a second slice cut from the same end of the specimen 

 as No. 783 (2). In many respects this slide is similar to the preceding, but there is a 

 little less hypersthene and garnet. The large crystals of apatite are still prominent, 

 and we have now noticed that the garnet rims may extend on to a crystal of 

 apatite. 



The garnet rims extend around the biotite-quartz aggregates in a manner noted 

 in the previous slide. Now the garnet, in addition to the rims, may extend as seams 

 through the aggregate in the same way that has already been seen in the hypersthene. 

 Further, the relic hypersthene in the same aggregates leaves no doubt whatever that the 



Serial A, VoL ra., Part 1 L 



