173 [Assembly 



due to different proportions in which the constituent minerals enter 

 into tliesc more common kinds of rocks, is wide and there is an almost 

 imperceptible degree of gradation from one to another. In the range 

 east of South Amenia there is a predominance of a fine, crystalline, 

 banded gneiss, which is in places highly micaceous, associated with a 

 grey granitoid gneiss. A very good section was examined between 

 Macedonia, Conn., and Dover Plains, crossing the East mountain. On 

 the eastern slope many ledges of dark- colored, muscovite-biotite gneiss 

 with syenite-gneiss were seen, traversed by dikes of coarse-crystalline, 

 grey-reddish granite. The latter rock has in places a gneissoid aspect 

 and doubtless there are on this slope some areas of unstratilicd granit- 

 oid gneiss. Near the top of the mountain there is more of this grey, 

 feldspathic, massive gneiss and granulyte, less of the micaceous, horn- 

 biendic varieties. The latter are much contorted in strike and appar- 

 ently much disturbed. Small masses of these varieties were observed 

 imbedded in the grey rock, indicating either very abrupt changes in 

 the conditions at time of formation, or, possibly, a breaking up of an 

 older series by the intrusion of eruptive masses. On the southern end 

 of this mountain there is a broad area, occupying nearly the whole 

 ■crest, of a peculiar-looking gneiss, consisting of flesh-colored ortho- 

 lase, white quartz and biotite. The feldspar and mica are arranged in 

 rudely parallel, thin layers, and the quartz is quite subordinate in 

 quantity. The feldspathic portions swell out into small lenticular 

 masses from one-half to an inch in diameter. They give the mass a 

 rough conglomerate, or rather a pseudo-porpliyritic aspect, suggestive 

 of the "augen gneiss" of German lithologists. There are no signs of 

 bedding in this rock of massive outcropping ledges, unless this mineral 

 2iarallelisni be taken as indicative of a stratification. And in the 

 mountain mass it may be considered as an unstratified rock ; in hand 

 specimens it has the appearance of gneiss. The same rock was ob- 

 served on the top of the range to the north and also on the " Cob- 

 ble" over the State line, in Connecticut. The outcrops of the west- 

 ern slope show as prevailing types, a dark-colored, fine crystalline, 

 syenite-gneiss, a muscovite-biotite gneiss and a grey, granitoid gneiss. 

 The variatioii in the strike of the strata of more schistose gneisses 

 on the west side also is remarkable, amounting to 30° within a few 

 yards, in places. Viewed as a whole the central j^art of the range 

 may be said to be mainly made up of grey, massive, unstratified 

 granitoid gneiss and granulyte, flanked on each side by the more 

 schistose and thin-bedded gneisses and mica schist, and the latter, 

 in turn, by the newer and unconformable quartzytic and quartz 

 schists. As compared with the rocks of Stissing mountain and the 

 Highlands of the Hudson, the rocks of this range have a more banded 

 or striped appearance ; they contain rather more black mica (biotite), 

 more flesh-colored feldspar, and in their strike there is more variation, 

 or more contorted. But these lithological distinctions are compara- 

 tively sliglit and apparently not sufficient to justify a division based 

 upon them alone. Hence the range is here placed as belonging in the 

 Archaean series and to the Highland belt.* 



* Prof. James D. Dana, iu bis papers on the Taconic rocks, published in the American 

 Journal of Science, has referred to the Dover-Keut-Cornwall range of gneiss and called it 

 Archaean.' — American Journal of Science (3\ vol. XVII, pp. 387-388; and vol. XXIX, pp. 

 ^14, 221. 



