GENERAL STRATIGRAPHY 



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intruded the gabbros and anorthosites of the Xorian. Purely litho- 

 logical names are here chosen to indicate these and they are subse- 

 quently described in what is believed to be their stratigraphical 

 succession. It would not be advisable to discuss at length this prob- 

 lem from the restricted area covered by this report. The difficulties 

 in accurate determination and classification rise from the intrusive 

 nature and vast extent of the Xorian. Near the contacts of the 

 undoubted gabbros and anorthosites with the gneisses there are all 

 manner of intermediate types of rock, and even far out from the 

 central masses, we find what are regarded as intrusive sheets of 

 gabbroitic gneiss, which possess the characters of both the gneisses 

 and the gabbros. It is hoped that by the close of the summer of 

 1804, that the whole of Essex co. will have been gone over once and 

 that then these questions can be more intelligently discussed. 



General character of the gneisses. The gneisses give little 

 decisive evidence of their origin, whether they have been derived 

 from sediments or from granitic rocks. Dr Smyth has shown the 

 latter to be true in the township of Gouverneur on the west side, 

 and the remarkable instances later described, by which the massive 

 gabbros have become gneissic, lends much support to this view for 

 many other regions. So far as they have been examined in the 

 townships specially noted here, they are aggregates of quartz, nor- 

 mal orthoclase, microcline, pyroxene, biotite, hornblende and great 

 quantities of microperthitic orthoclase. The last named is rather 

 the most abundant component. It consists of orthoclase crystals so 

 thickly set with blades of albite that at times they almost seem like 

 crystals of banded plagioclase. Such structures are well known in 

 both igneous granites and metamorphic gneisses. At times, specially 

 near the Bessemer iron ores the gneiss becomes a nearly pure mix- 

 ture of quartz and feldspar. 



General characters of the crystalline limestones. The lime- 

 stones are variable in structure and composition. They are in 

 instances extremely pure carbonate of lime. The quarry opened 

 for the Port Henry furnaces, a quarter of a mile north of Port 

 Henry and east of the Treadway ophicalcite quarry was of this char- 

 acter. But here as elsewhere great bunches of silicates came in and 

 necessitated much waste. It is rare that a bed of any size is met, 

 which is not limited on either side by a black, hornblendic schist or 

 gneiss. The exposed cross-sections show this alteration over and 

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