12 ROYAL SOCIETY OF CANADA 



The shells or raantles of muscovite which often enclose the in- 

 dividuals of corundum are distinctly and clearly attributable lo me in- 

 creased acidity and hydration of the magma in its later stages. 



The nepheline syenites and the associated alkali syenites occur al- 

 most invariably on the borders of the granite biathyliths where these cut 

 through crystalline limestone. 



When the actual contact of the two rocks is well exposed, large in- 

 dividuals of nepheline, biotite and other constituents of the syenite can 

 be seen to have developed in the limestone all along the margin of the 

 nepheline syenite body, while masses of the limestone, groat and small, 

 can be found scattered through the nepheline syenite along the contact. 

 These masses, furthermore, were evidently in process of replacement by 

 the magma, the various constituents of the nepheline syenite growing 

 into them. They thus become gradually reduced in size, and now survive 

 merely as sepairate, irregularly rounded grains of calcite often enclosed 

 in single individuals of perfectly fresh nepheline, hornblende or other 

 minerals of tlie nepheline syenite, or lying between these, with the form 

 of the latter impressed upon them on every side. (See Plates 4 

 and 10). 



Every stage of the passage from the solid limestone to the separate 

 calcite grains enclosed in the constituent minerals of the nepheline 

 syenite can be distinctly traced, while the latter is at the same time fresh 

 and free from decomposition products. The phenomenon is well seen in 

 the railway cutting on the outskirts of the village of Bancroft. In some 

 cases an additional proof of the derivation of the calcite from the ad- 

 jacent limestone is afforded by the fact that the calcite grains enclosed 

 in the nepheline syenite show the twisting and the strain shadows to be 

 observed in the constituent individuals of tlie invaded limestone, while 

 the minerals of the nepheline syenite which enclose them, are absolutely 

 free from all signs of pressure. The calcite in the syenites is therefore 

 undoubtedly foreign to the magma and represents inclusions of the sur- 

 rounding limestones. In the case of the only important body of nepheline 

 syenites which does not have limestone as a wall rock, namely the occur- 

 rence in the township of Methuen, calcite is vei^; rarely found in the rock, 

 and when it does occur, it is in very small amount, while the mode of its 

 occurrence is entirely different from that above described and is such as 

 to indicate tliat the mineral is probably secondant or a later infiltration. 



The presence of calcite has been noted in other occurrences of 

 nepheline syenite. These are like those of the area at present under dis- 

 cussion, associated with ancient metamorphic rocks, but the calcite in 

 them is believed to be primary by the investigators who have studied 



