MICA-APATITE HORIZON. 485 



view has doubtless arisen from an imperfect study of both the limestones 

 and pyroxene, the latter in the earlier stage of the investigations on these 

 rocks being regarded as a peculiar variety of the sedimentary gneiss 

 formation, as already pointed out, while concerning the former it is 

 found that in many of the pyroxene dikes, more particularly near their 

 contact Avith the grayish gneiss, an irregular development of calcite, gen- 

 erally of pink color, occurs, w^hich by the miners is styled a limestone, 

 and has thence been confounded with the distinctly different limestone 

 formation which forms the upper portion of the Laurentian system. In 

 no case can this calcite, in which very frequently the mica crystals, as 

 well as crystals of apatite, are disseminated, be regarded as a member of 

 the sedimentary or stratified Laurentian series, but is always found as 

 an irregular, generally pockety, mass in the intrusive pyroxene. 



Mica- Apatite Horizon. — The horizon of these deposits, both of mica 

 and apatite, can now be very clearly defined. They are for the most part 

 confined to the series of gneisses which constitute the upper portion of the 

 Laurentian silicious rocks and which underlie the limestone proper. 

 These gneisses are generally of some shade* of grey, with reddish grey, 

 reddish and hornblendic bands, some of which are garnetiferous, and 

 nearly all of which contain a large percentage of silica in the form of 

 quartz. These beds, as already pointed out, graduate upward by regular 

 passage through the interstratification of calcareous layers into the mas- 

 sive crystalline limestone formation. In the Buckingham and Templeton 

 areas apatite and mica are rarel}^ found in dikes cutting calcareous strata, 

 but in the G^^tineau area several localities are known where large dikes of 

 pyroxene in limestone carry mica in workable quantity. 



Mica deposits generally occur in the form of crystals, some of which 

 reach an enormous size, instances being lately reported of single crystals 

 measuring nearly eight feet across the face. These crystals sometimes 

 occur in the pyroxene in pockety masses distinct from each other, or in 

 somewhat irregular deposits near the contact of the enclosing pyroxene 

 and the gneiss adjacent or as scattered crystals through the mass of the 

 dike itself, but generally near the contact. In many cases of pyroxene 

 dikes where the mica occurs as a contact deposit near the gneiss it is 

 found associated with masses of pink calcite, some of which are but of 

 small extent, while others have a thickness of several feet and are tracea- 

 ble for some yards. The mica found in the calcite is, as a rule, in well 

 formed crystals disseminated through the mass, and often associated with 

 well terminated crystals of apatite. In some cases the latter penetrate 

 the former, while frequently inclusions of calcite or apatite are found 

 in the center of the mica crystal. Of the mica found in the mass of the 

 pyroxene it may be said that the crystalline structure is rarely perfect. 



