58 



After the intrusion of the Taurentian there was a pro- 

 longed period of erosion, and the Hastings sedimentary- 

 series, consisting of conglomerate and other rocks, was laid 

 down. 



Finally all the older rocks were invaded by the Moira 

 granite and felsite, and later by basic dikes. 



On the surface of the pre-Cambrian rests the Black 

 River limestone, the lower formations of the Ordovician 

 being absent in the district. 



The accompanying colored map, scale 1,000 feet to the 

 inch, shows the distribution of the rocks in the Madoc 

 area. 



ECONOMIC MINERALS. 



Taec. A large body of talc is located on the southern 

 outskirts of the town of Madoc. The deposit occurs in a 

 brown, somewhat quartzose crystalline limestone of Gren- 

 ville age, an analysis of which shows it to have the following 

 composition: Ca O, 29.29 per cent.; Mg O, 15.53 P er cent.; 

 C O, 43.67 per cent. ; insoluble, 4.62 per cent. The talc has 

 a width which varies from 25 feet or less to 40 feet. The 

 crystalline limestone on each side of the deposit con- 

 tains bands of white quartz several feet or more wide. 

 A horizontal plan shows the talc to occur in the form of a 

 horseshoe, or the letter " V," due to the strata having been 

 sharply folded. The material has been mined a distance 

 of about 500 feet, but the extent of the body has not yet 

 been determined in the underground workings ; and the sur- 

 face on each side of the hill is covered with drift. 



It is probable that the talc has resulted from the altera- 

 tion of the crystalline limestone, since many parts of the 

 occurrence still show distinct traces of the original bedding 

 or lamination of the limestone. The origin of the talc may 

 be partly connected with the intrusion of the Moira granite 

 from which circulated silica holding waters. The latter 

 probably acted on the dolomitic limestone, giving rise to 

 the hydrated, magnesian silicate, talc. 



Pyrite. The pyrite mine of the Canadian Sulphur Ore 

 Company is situated several miles northeast of Madoc near 

 the village of Queensboro. The ore body occurs in Gren- 

 ville rocks at the contact of a bed of fine-grained, rusty schist 

 and quartzite, both beds resting in almost vertical position. 



