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schist, which lies between the two in the southeast corner of the 

 Alexandria sheet, and which consists of alternating bands of quart- 

 zite and various schists of no enormous individual thickness, but 

 which, taken together, must have a thickness of several - thousand 

 feet, rests upon the thick limestone and is the youngest portion of 

 the Grenville exposed within the map limits. To the north, and be- 

 neath the limestone would come the great complex of green schists 

 and impure greenish limestones which there occurs, which have 

 steep dips and must have large thickness, at least as great as the 

 two previous groups, and likely greater. Doubt is thrown, however, 

 upon this interpretation by the fact that the rocks which follow the 

 thick limestone to the south, on the Theresa sheet, differ consider- 

 ably from the green schist series which follows it to the north on 

 the Alexandria sheet, and yet according to this interpretation the 

 two should be identical, representing the series directly beneath 

 the thick limestone. Each does consist of schist, calcareous schist, 

 and thin limestone bands, with an occasional thin quartzite, but the 

 Theresa rocks are not of this distinct green schist type. A possi- 

 ble answer to this objection may be found in the fact that, not- 

 withstanding a rather intimate acquaintance with the Grenville 

 series all over northern New York and in parts of Canada, the 

 writer has nowhere else seen the counterpart of this green schist 

 series. It is in rather close association with the Picton granite, 

 which was richly supplied with mineralizing agents, and is every- 

 where cut with numerous dikes from this granite, so that its pecu- 

 liar characters are thought to be largely, or wholly attributable to 

 this contact action, and thus explained as due to these local condi- 

 tions. If this be not the explanation there seems no alternative 

 but to regard the two thick limestones as separate beds, thus largely 

 increasing the thickness of the section, already great. If the struc- 

 ture is thus correctly interpreted, a thickness of at least 20,000 feet 

 is indicated for the Grenville of the district, and this is a conser- 

 vative estimate. If the structure is not synclinal this thickness 

 must be nearly doubled. 



This matter will be discussed somewhat more in detail on a later 

 page. The purpose here is simply to give an outline of the sup- 

 posed Grenville succession and some idea of the great thickness 

 of the series. 



Limestones. The general Grenville limestone of the district is 

 a coarsely crystalline and quite pure white marble, only sparingly 

 charged with other minerals. The great bulk of the rock of the 

 thick belt, or belts, just referred to, consists of 95$ or upward of 



