62 NEW YORK STATE MUSEUM 



it out lies in the assignment of the silica after the orthoclase and 

 albite have been cared for. In order to have enough to combine 

 with the bases, all the magnesia was necessarily assigned to olivine, 

 as was the ferrous iron except what was required for magnetite. 

 The remaining silica was then divided between anorthite and augite. 

 For the lattter, the molecule CaO.AUOg.SiOg was necessarily used 

 with CaO.SiOs- It is probable that this gives too little anorthite and 

 that the magnesia and ferrous iron are not all in the olivine. If so, 

 the necessary silica can only be found by assigning some soda to 

 the pyroxene. There is undoubtedly some kaolin and chlorite, pos- 

 sibly also some serpentine, but there is no means of assigning the 

 water. The proportions of light and dark minerals are doubtless 

 near the truth. 



Chapter 5 



PALEOZOIC STRATA 



Potsdam sandstone. This formation occupies nearly the whole 

 of the Paleozoic fringe about Port Henry. It also constitutes a 

 small fault block at the south end of the Westport area, and it 

 further appears at the north end of the latter in the bed of Ham- 

 mond brook in Westport village from beneath the Beekmantown 

 beds. 



The former extension of the Potsdam formation over all or the 

 greater portion of the Elizabethtown and Port Henry sheets is 

 clearly demonstrated by a small outlier observed by Pro'fessor 

 Kemp far back in the mountains. Professor Kemp writes on this 

 exceedingly interesting outlier : 



The Potsdam outlier consists of cream-colored or yellowish 

 quartzite, in beds of several inches thick. The strike is n. 20° w., 

 dip I3°e. 12 feet are clearly exposed in one place with no bot- 

 tom shown, and probably not less than 25 feet are present, perhaps 

 more. The exposure extends 100 yards at least. It lies in the 

 drainage of the Schroon river, down which and 12 or 13 miles to 

 the south is a block of Beekmantown limestone on which is built 

 the village at Schroon Lake post office. This is the nearest of the 

 other Paleozoic exposures. 



Another outlier farther north is indicated by the following ob- 

 servations of Professor Kemp : 



Again in the area colored for basic anorthosite and i^ miles 

 northwest of Elizabethtown and near the boundary with Lewis, 

 loose slabs of Potsdam sandstone have been found in such abund- 

 ance that they have been used for building stone in one or two of 

 the finest residences in Elizabethtown. Careful search along a 

 small affluent of Barton brook revealed many loose pieces, strongly 

 suggesting an outlier in place, but no actual ledge could be located. 



