216 Canadian Record of Science. 



Bearing in mind, therefore, the fact that the Laurentian 

 rocks must be regarded as divisible into two distinct 

 groups, we find from their study in the field, certain 

 features in regard to the occurrence of apatite which serve 

 to throw much light upon its early history. It may be 

 very conclusively stated, that for the most part at least it 

 is confined to pyroxenic rocks, although certain writers 

 have asserted that it is found equally in the stratified gneiss 

 and limestone formations. It may, however, be said that 

 after a careful study of all available openings in the Ottawa 

 district, no locality has yet been seen where apatite occurs 

 in workable quantity, or in fact in any way except as 

 occasional scattered crystals in either the limestone or 

 gneiss. The conflicting statement as to its presence in the 

 limestone seems to have arisen largely from the occurrence 

 in many of the pyroxene dykes of masses of calcite, gen- 

 erally of a pinkish color, some of which are of large ex- 

 tent but all strictly integral portions of the pyroxene, 

 through which scattered crystals of mica and apatite are 

 distributed, and it is from this calcite that the most perfect 

 crystals of both these minerals are obtained. 



The confusion as to the mode of occurrence has there- 

 fore in this case presumably arisen from a lack of care on 

 the part of the earlier observers in separating the mineral 

 calcite from the limestone formation proper, which is en- 

 tirely different in character and has evidently been formed 

 in an entirely different manner. The reputed occurrence 

 in gneiss can also be traced to the opinion formerly held 

 regarding the nature of the pyroxene bands, which re- 

 garded these as of purely sedimentary origin and as consti- 

 tuting a regularly inters tratified portion of the gneiss forma- 

 tion, where it was known under the name of pyroxenic 

 gneiss. In the limestone formation proper occasional 

 small crystals of apatite are found where small dykes of 

 pyroxene penetrate the rock, and still more rarely crystals 

 occur in that portion of the gneiss in close proximity to the 

 intrusive mass. 



As regards the mode of occurrence of the pyroxene itself 



