176 [Assembly 



the slates and drift. It is five miles in length ; its breadth nowhere 

 exceeds one-third of a mile, being greatest in the Tillage of Glenham, 

 where the Reformed church stands on the north margin and the 

 Public or Union School-building is near the south side of the outcrop. 

 At the north-east end, Vly mountain represents its breadth. Through- 

 out its surface is rocky, but it is not very prominent above the adja- 

 cent formations of slate and limestone, excepting in Vly mountain 

 where it attains an elevation of 250 to 300 feet above the Fishkill 

 plain. The formation on the north-west is a bluish-black slaty rock, 

 but it was not found cropping out near enough to this crystalline rock 

 to indicate its true relation to the latter. The blue limestone bounds 

 it on the south-east. And the beds of this rock dip south-east or from 

 the granitoid rock, but the CDBeealed distances between their outcrop 

 (nowhere less than 100 feet) are too great to permit any conclusions 

 as to their exact position in reference to one another. There is doubt 

 about the crystalline rock being stratified. The only locality where 

 it appears to have bedding is near Glenham, and the dip is there 

 nearly vertical north 10°-15° east. But the parallelism in the min- 

 erals is all that is evidence of stratification. 



There are two principal varieties of rock in this short and narrow 

 outcrop. One is a pinkish-colored granite, consisting almost wholly 

 of orthoclose and a milk-white quartz. It has a little brown mica in 

 small, scattered scales through its mass. The other variety is a green- 

 ish-grey rock made up of a triclinic feldspar, orthoclose, white, opaque 

 quartz and a very little black mica and hornblende. Inasmuch as the 

 prevailing types of rock are unlike the characteristic varieties of crys- 

 talline rock in the Fishkill mountain so near on the south there is 

 doubt about classifying this little belt with the Highlands. And it 

 is placed here provisionally until the district can be more thoroughly 

 studied and the rocks be examined microscopically.* 



The south-eastern boundary of the Highlands Archasan rock may be 

 described as having a general southerly course from Gardiner's Hollow 

 near Poughquag in Dutchess county, to Towner's Station in Putnam 

 county, and a south-west course from the Connecticut line, east of 

 Brewsters, by Croton falls, JeSerson valley. Shrub Oak and Oregon 

 to Peekskill Bay at Annsville. The rock of the adjacent formation 

 throughout much of this distance is mica schist. Near Oregon, there 

 is a very fine-grained, black, hydro-mica schist and the same rock 

 continues bordering the gneissic outcrop thence more or less all the 

 way to the Peekskill cove. On the Hudson river, the nearest ledges 

 to the gneiss, which crops out on the north of the cove, are south-east 

 dipping strata of greyish quartzite and a feldspathic quartzite in the 

 bluif between the cove and Peekskill. 



Beginning at the north-east, in Gardiner's Hollow, north-east of 

 Poughquag, the eastern limit of the Archaean gneisses coincides with 

 a slight surface depression Avhose general course is south 20° west 

 (magnetic) from the so-called "Dug road" to the Beekman and Paw- 



*Thi3 rock was called an " altered sandstone" by Prof. James Hall and Sir William 

 Logan, in a paper read before the Natural Historv Society of Montreal, Oct. 24, 1864, by 

 T. Sterrv Hunt. See Am. Jour, of Science (2), vol. XXXIV, p. iifi. 



Prof. "Dana calls it a " granite-like stratum" and a stratified formation, in his descrip- 

 tion of the laconic schists and associated limestones m that part of Dutchess county. Am. 

 Jour, of Science (3), XVII, p. 386. 



