F. D. Adams — New Nepheline Rock. 271 



the township of Dungannon, to the east of the village of Ban- 

 croft. 



These nepheline syenites occur cutting the rocks of the 

 Grenville series, which consist largely in this district of crys- 

 talline limestones. Their wall rock consequently in almost 

 every case is limestone. The only occurrence which is not 

 directly associated with large masses of this rock is a large iso- 

 lated intrusion in the township of Methuen, where the country 

 rock is granite and amphibolite, the latter holding only a few 

 small limestone bands. 



With this is connected one of the most curious phenomena 

 presented by these nepheline syenites, namely, the presence in 

 them almost everywhere of calcite. This calcite when appear- 

 ing in the analysis of a rock at once suggests an advanced stage 

 of alteration, since calcite when found in igneous rocks is almost 

 invariably a secondary product. In other cases calcite in plu- 

 tonic rocks has been supposed to occupy miarolitic druses and 

 to have been deposited in these by percolating waters. 



A very careful examination, however, of the calcite-bearing 

 occurrences of nepheline syenite in the various parts of this 

 area has clearly shown that in the case of these rocks the cal- 

 cite represents inclusions of the crystalline limestone penetrated 

 by the intrusion, a fact which receives additional substantiation 

 in the fact that in the Methuen occurrence, when the wall 

 rock is not limestone, the nepheline syenite does not contain 

 calcite. Along the borders of the intrusion, the nepheline 

 syenite is seen to eat into the limestone and to enclose large 

 masses, the constituent minerals of the syenite growing into 

 the substance of the limestone, often with well defined crystal 

 terminations. These masses often show a coarsening in grain 

 as a result of the metamorphic action of the intruding rock. 

 On receding from the contact, the inclusions become less numer- 

 ous and smaller, and eventually the large masses are disinte- 

 grated into separate individuals of calcite or small groups of 

 calcite grains. These, under the microscope, can be seen as 

 rounded, often perfectly round, inclusions completely enclosed 

 in a single individual of nepheline or other constituent of the 

 nepheline syenite, or lying between other constituents of the 

 rock, which latter can be seen to have grown into the calcite. In 

 these cases all the minerals are perfectly fresh and unaltered, 

 and, while the constituent minerals of the nepheline syenite 

 rarely show pressure phenomena, the calcite individuals are 

 often seen to be much bent and twisted and to display marked 

 strain shadows, the movements displayed being those which 

 overtook the limestone before the intrusion of the syenite 

 into it. 



It being, therefore, clearly recognized that the calcite is some- 



