[ADAMS à barlow] ALKALI SYENITES OF EASTERN ONTARIO 75 



5. All phases of this magma were in certain localities super- 

 saturated with alumina, which when the magma was low in MgO and 

 FeO, crystallized out as corundum, giving rise to several new rock 

 types, three of which, Eaglanite, Craigmontite and Dungannonite are 

 described in this paper. 



The development of corundum from these magmas follows the law 

 established experimentally by Morozewicz in his researches on molten 

 magmas. 



6. Another striking feature presented by the nepheline syenites of 

 the district under discussion is the frequent appearance of very 

 coarse grained or pegmatitic developments of the rock. The constituent 

 individuals are in many places a foot in diameter, while on the York 

 branch of the Madawaska river, in the township of Dungannon, wher^i this 

 stream is crossed by the road running east from Bancroft, the rock con- 

 tains individuals of nepheline two and a half feet in diameter, while 

 masses of pure nepheline a yard in diameter are found in the nepheline 

 pegmatite on lot 30 of range VI of the township of Glamorgan. These 

 pegmatitic developments in some eases have the form of dykes cutting 

 the normal nepheline syenite or some other rock, but elsewhere they are 

 very coarse grained masses or " flammen " in the finer grained nepheline 

 syenite, apparently of the nature of " contemporaneous veins '' and cor- 

 respond to the developments of pegmatite so often found in connection 

 with granite. 



7. The nepheline syenite occurs almost invariably along the border 

 of the granite intrusions where they cut limestone. When the actual 

 contact of the nepheline syenite and limestone can be seen, masses of 

 the limestone, great and small, are found scattered through the nepheline 

 syenite along the contact. These masses are in course of replacement by 

 the magma, and at a distance from the contact are seen to be greatly re- 

 duced in size and often disintegrated. Still further from the contact 

 they are represented by irregularly rounded grains of calcite lying be- 

 tween the perfectly fresh individuals of the several constituent minerals 

 of the nepheline syenite, or, in some cases, actually as inclusions in these 

 minerals. 



8. For convenience of reference the twelve analyses of the nephe- 

 line and alkali syenites of this region which have been given in this paper 

 are tabulated below. These include analyses of the four new rock types 

 described. 



