248 GEOGNOSY OF THE APPALACHIANS. [XIII. 



older underlying rocks belonging, not to the palaeozoic system, 

 but to our second series of crystalline schists. We conclude, 

 then, that while the gneisses to the northwest, and probably 

 those along the southeast rim of the mesozoic basin of Penn- 

 sylvania, are Laurentian, the great valley southward to the 

 Delaware is occupied by the rocks of the Green Mountain 

 and White Mountain series. The same two types of rocks, 

 extending to the northeast, are developed about New York 

 City, in the mica-schists of Manhattan and the serpentines of 

 Staten Island and Hoboken ; while in the range of the High- 

 lands, the Laurentian gneiss belt of the South Mountain 

 crosses the Hudson River. 



The three series of gneissic rocks which we have distin- 

 guished in our section to the northward have, in southeastern 

 New York, as in Pennsylvania, been grouped together in the 

 primary system, and may thence all be traced into western 

 New England. In Dr. Percival's Geological Report and Map 

 of Connecticut, published in 1840, it will be seen that he 

 refers to the gneiss of the Highlands two gueissic areas in 

 Litchfield County ; the one occupying parts of Cornwall and 

 Ellsworth, and the other extending from Torrington, north- 

 ward through Winchester, Norfolk, and Colebrooke into Berk- 

 shire County, Massachusetts. Further investigations may 

 confirm the accuracy of Percival's identification, and show the 

 Laurentian age of these New England gneisses, a view which 

 is apparently supported by the mineralogical characters of 

 some of the rocks in this region. Emmons informs 'us that 

 primary limestones with graphite (perhaps Laurentian) are 

 met with in the Hoosic range in Massachusetts east of the 

 Stockbridge (Taconic) limestones. 



The rocks of the second series are traceable from south- 

 western Connecticut northward to the Green Mountains in 

 Vermont, and the micaceous schists and gneisses of the third, 

 or White Mountain series are found both to the east and the 

 west of the mesozoic valley in Connecticut and Massachusetts. 

 They also occupy a considerable area in eastern Vermont, 

 where they are separated from the White Mountain range by 



