part 3] MINOE INTRUSIONS IN THE ISLAND OF MULL. 259 



Plate X. 



Fig-. 1. Sillimanite-buchite invaded by magma, with the resultant 

 formation of large crystals of cordierite in a dark giassy matrix 

 charged with acicular crystals of felspar, which range from 

 labradorite to oligoclase in composition. The cordierite- crystals 

 contain sillimanite-needles which are identical with those of the 

 buchite, and are evidently the undissolved residue of the same. 

 The sillimanite is pale pink in both cases. Shore 700 yards 

 south-west of Tiroran. S. 18532. X 18. (See p. 246.) 



2. Shows the formation of beautiful crystals of cordierite (partly pmi- 



. tized) as the result of the reaction between the igneous magma and 

 a sillimanite-buchite. The cordierite-crystals are large and well- 

 formed next to the buchite, but smaller and full of spinel nearer to 

 the true igneous rock. Pink sillimanite occurs as in the above 

 cases, and is obviously of earlier formation than the cordierite. 

 Coast 3500 feet slightly north of west of Ormsaig-. X 9. (See 

 p. 246.) 



3. This rock consists of an aggregate of anorthite- crystals (large colour- 



less area) that contain small sapphires and a plum-coloured spinel. 

 The anorthite has suffered resorption with the subsequent crystal- 

 lization of labradorite upon its edges. Large cordierite-crystals, 

 free from inclusions and often exhibiting beautiful twin- structure, 

 have developed in the magmatic matrix. One such crystal of 

 cordierite occupies the centre of the field. Slightly north of west 

 of Ormsaig. S. 18003. X 17, crossed nicols. (See p. 246.) 



4. Brecciated anorthite - xenolith invaded by magma, with 



attendant resorption. The part of the section figured shows the 

 result of the resorption of the original xenolith in the precipitation 

 of large, well-shaped, reddish plum-coloured spinel, crystallization of 

 feathery oligoclase-andesine, and the formation of large rectangular 

 crystals of cordierite in a glassy matrix. North of Feorlein Cottage, 

 Carsaig. S. 18493. X 25. (See p. 248.) 



5. Edge of a sillimanite- anorthite xenolith acted upon by magma, and 



showing the regrowth of basic felspar on the resorbed anorthite. 

 Spinel and less basic lath-shaped plagioclase have formed in a 

 glassy matrix. Note the circular form of an amygdale in the 

 upper part of the figure. E,udh' a'Chromain. S. 16601. X 15. 

 (See p. 245.) 



6. This shows the brecciation of the primary sillimanite-bearing an- 



orthite, its partial resorption by magma, and the concomitant 

 precipitation of a plum- coloured spinel and oligoclase in a glassy 

 matrix. North of Feorlein Cottage, Carsaig. S. 18492. X 18. 

 (See p. 254.) 



Discussion. 



Sir Jetheo Teall said that, so far as he knew, this was the 

 most perfect case oi its kind that had ever been described. The 

 paper was evidently of great interest and importance. 



Mr. G-. Baerow congratulated the Author on the valuable 

 results of his work on the inclusions of sedimentary material 

 caught up in a volcanic magma at a great depth below^ the 

 surface. The evidence produced by the Author seemed to indicate 

 clearly that the mineralogical changes had been produced at a 

 considerable depth. The Author was fortunate in having to deal 

 with a material that from its composition could only have been a 

 pure shale originally. The distinctive minerals are the same as 



