1902J Barlow Nepheline Rocks of Ice River, B.C. 71 



is believed to come within about four miles of the Canadian Pacific 

 Railway between Ottertail Crossing- and Leanchoil stations. 

 Thence with an approximate width of two miles it extends for a 

 distance of about sixteen miles, the strike of the belt gradually 

 bendingf around in this interval from southeast to east. As far 

 thus as our present knowledge goes, the area underlaid by these 

 rocks is about thirty-two square miles. 



The hand specimens which were made the subject of examina- 

 tion and study, were of necessity collected rather hurriedly, and 

 were chosen simply as representative of the several varieties of 

 igneous rocks seen to occur at this locality. It is therefore a very 

 agreeable surprise to find that the material thus selected at a time 

 when magmatic differentiation was very little understood, should 

 illustrate a passage so complete that no appreciable gap occurs 

 unrepresented by specimens from the most basic ijolite containing 

 36,988 per cent, of silica to sodalite syenite or foyaite with 53,638 

 per cent, of silica. A large number of thin sections were prepared 

 from the material at command as it was believed that considerable 

 information would be gained by their study under the microscope 

 regarding the phenomenan known as magmatic differentiation, 

 which it is confidently believed is so well represented at this 

 locality. Perhaps one of the most significant developments in 

 petrographical geology during the last few years has been the 

 enunciation of the principle, that no sharp line of delimitation 

 exists between what has hitherto been regarded as the main 

 types of families of igneous rocks, but that these merge by insen- 

 sible g;radations into one another. Many of the preexisting gaps 

 have of very recent years been so well bridged by hitherto unknown 

 species that it is now certain that at no very distant date, such 

 sequences will be practically perfected by the recognition and 

 description of the various transitional types now lacking. Repeated 

 and conclusive observations have likewise shown that no consider- 

 able area of igneous rocks occurs without furnishing some proof 

 of this diversity in composition, so that at the present time it is 

 considered the exception rather than the rule, to meet with any 

 extended rock exposure which does not give some evidence of such 

 gradation of one rock type to another. 



