4 SUBDIVISION OP THE LAtTRENTIAN ROCKS Of CANADA. 



Bands of dolomite sometimes accompany the limestone which is 

 often iuterstratified with bands of quartzite. The quartzites appear 

 to be heaviest near the junction of the limestone and gneiss, becoming 

 thinner and less frequent as we recede from the calcareous rock. 

 The greatest mass of quartzite met with, had a Tertical measure of 

 400 feet, and it was in stratigraphical position beneath the limestone. 

 The quartzite and the gneiss on each side of the limestone are often 

 very thickly studded with garnets, and in some cases the aggregation 

 of these is so close as to constitute a granular garnet rock. In the 

 G-ore of Chatham a band of limestone about three-fourths of a mile to 

 the north-west of the one described, has been traced running parallel 

 with it for seven miles. If the form which has been attributed to the 

 first band be correct, the second would overlie it, with a great mass 

 of gneiss between. A third band of limestone occurs about six miles 

 north of the second ; this has been traced for about four miles run- 

 ning east, which would be nearly parallel with the bearing of the 

 second. In this bearing it has not yet been followed farther than to 

 within a short distance from the line between the Seigniory of Argen- 

 teuil and the township of Abercrombie, towards the rear of both. 

 i; Continuous exposures of limestone have been met with on the west 

 side of the Eiviere du Nord, at St. Jerome. They have been follow- 

 ed for two iriiles with a aorth bearing, and the strike of the stratifi- 

 cation between Saint Jerome and the rear of Abercrombie, is such as 

 to make it probable that the St. Jerome rock will ultimately prove to 

 be a part of the third band. A feature common to both localities ia 

 the occurrence immediately near the limestone, of immense masses of 

 lime feldspar. North of the Argenteuil band, eight miles, examined 

 across the stratification, consist almost entirely of it, in the form of 

 labradorite, of which masses of the opalescent variety are in some 

 parts enclosed in a paste of mineral without any play of colors. These 

 feldspars are accompanied with hypersthene and ilmenite. This feld- 

 spar rock is abundant at St. Jerome, and its stratified character is 

 conspicuously displayed, the beds running parallel with the limestone. 



Mr. Hunt has traced a band of crystalline limestone for eleven 

 miles, running diagonally across the township of Kawdon in a north 

 bearing. On the west side of this, lime-feldspar forms the great bulk 

 of the rock exposures for twelve miles across th© measures, and 

 shows a well-marked stratification. It appears probable that the 

 Eawdon calcareous band is the same as the St. Jerome band, and 

 ■that a synclinal axis exists between the two, the turn of the calcare- 

 ous band on which is covered up by the fossiliferous rocks to the south. 



