126 Transactions. 



the minerals of the groundmass present the same relations to 

 both the amphibole and the pyroxene, the amphibole may be a 

 secondary mineral, and possibly the augite sometimes passed 

 over to serpentine and sometimes to hornblende. 



34. Has a tinguaitic groundmass typical of this series, con- 

 sisting of nepheline, cancrinite, and feldspar — much of which 

 is perthite — with aegerine microlites. With the exception of 

 the segerine, the minerals of the groundmass are allotriomorphic. 

 The rock contains well-developed phenocrysts of hornblende, 

 in long needles and as prisms with polygonal boundaries, and 

 also augite in prisms. There are large phenocrysts of perthite 

 with marginal corrosion and of anorthoclase undergoing altera- 

 tion to muscovite. (Plate XVIII, fig. 7.) 



107. Is a similar rock to 114, but contains some remark- 

 able examples of leucocrasia. Megascopically the appearance 

 of the rock is peculiar, the tinguaitic portion being dark-grey 

 to black in colour, whilst the leucocratic patches are almost 

 white. In the field the white portions were mistaken for parts 

 of the intruded rock attached to or included in the intrusive, 

 but a section cut across what appeared to be the junction 

 shows that such is not the case. The white rock consists of a 

 hypidiomorphic even-textured aggregate of anorthoclase, the 

 plates frequently measuring 2 mm. in diameter, and enclosing 

 ophitically but sparingly ragged crystals of green common 

 hornblende. The larger phenocrysts of feldspar in the tingu- 

 aitic portion are undergoing alteration to muscovite. (Plate XIX, 

 fig. 11.) 



32. Tinguaite porphyry. Though the previously described 

 rocks are porphyritic by a recurrence of the feldspars in two 

 generations, this is the first example in which the recurrence 

 takes place with the essential mineral, the nepheline. Without 

 the nepheline phenocrysts the rock is similar in all respects to 

 No. 114, including the serpen tinous mineral after augite. The 

 porphyritic nephelines form good hexagonal tables, 1 mm. to 

 1£ mm. in diameter. (Plate XVIII, fig. 6.) 



With the disappearance of the nepheline and cancrinite the 

 rocks pass into the family of the lamprophyres. Some of these 

 have been classified as vogesites and others as camptonitos. 

 It will be noticed that those in which the dominant feldspar- 

 is anorthoclase have been classed as vogesites, which may not 

 be strictly correct. 



49. Vogesite. A groundmass of shapeless elongated and 

 ragged crystals of anorthoclase, enclosing microlites, needles, 

 lath- and blade-like crystals and polygonal tables of augite and 

 hornblende. Many of the colourless augites and pale-brow n 

 hornblendes are surrounded by a resorption border of aegerine 



