BY W. H. TWELYETREE8 AND W. F. PETTERD. 57 



the slate, a quartzo-felspathic variety, is micaceous, with 

 chlorite and actinolite. Leaying' the metals out of con- 

 sideration, the dyke is composed of monoclinic pyroxene 

 (largely altered to uralite and actinolite) axinite, calcite, 

 datholite, danburite, with a little secondary quartz (?) 

 chlorite and granular sphene, and a little talc in the rock 

 •occurring further north on the Clifton property. We 

 are disposed to consider the pi-esence of original horn- 

 blende not established. The axinite is in veins and 

 massive patches, and is intergrown with datholite, dan- 

 burite, and the other minerals of the rock mass. 

 Professor A. Lacroix, in his memoir on the limurite of the 

 Pyrenees, is of opinion that the rock does not belong to a 

 definite petrographical type, as it is variable in structure, 

 and its mineralogical composition differs in different parts 

 of the same mass. This remark applies with unabated 

 force to the Colebrook intrusion, so far as the dyke as. a 

 unit is concerned. Looking at it in this way, it is 

 essentially a pyroxenite, which here and there receives the 

 addition of axinite and other boi'ic minerals. Where these 

 minerals are develo])ed the rock l)ecomes localh' limurite, 

 a composite rock containing pyroxene and axinite. It is 

 agreed that the axinite I'esulted from l>oric emanations, but 

 how these were introduced is matter for speculation. Was 

 the magmatic reservoir below an independent unit in course 

 of differentiation into basic and acid layers at the time of 

 intrusion ? Or was this spot on the confines of two reser- 

 voirs, and were the boric vapours, which were carried up 

 in the pyroxenic material, escapes, so to speak, from the 

 neighbouring acid basin 'i Axinite veins are often found 

 elsewhere injected into rocks already consolidated, l)Ut in 

 this case it seems clear that the two elements crystallised 

 synchronously. Even in those parts which are veined ])y 

 -axinite we do not think that the veining was later than 

 the consolidation of the mass as a whole, nor that the rock 

 as a whole had emerged from the phase to which both 

 pyroxene and boron vapours alike belonged. One part of 

 the intrusion may very well have advanced a little further 

 in the crystallising process while other parts lagged 

 behind ; and one result of this would be the somewhat 

 heterogeneous character of the dyke as a whole, which, in 

 fact, we observe. 



That there was a granite reservoir not far off is shown 

 by the tourmaline-quartz porphyry to the west at the 

 South Renison Bell mine, l^etween which and the Cole- 

 brook is another occurrence of axinite, in the form of 



