GEOLOGY OF THE CONNECTICUT VALLEY DISTRICT. 429 



low, being rarely elevated very much above the alluvial deposits. Upon 

 the general map the latter occupy a large part of the space properly be- 

 longing to the gneiss. Ledges may crop out beneath a sand bank just 

 enough to indicate the nature of the solid foundation, but not sufficiently 

 to be colored upon a map of so small a scale as two and one half miles to 

 the inch. Our special enlarged map will not be encumbered unnecessa- 

 rily by the surface deposits. The basin-shaped appearance of the Hel- 

 derberg section has been already alluded to in our chapter on Topogra- 

 phy, while the recently prepared contour lines exhibit the details. There 

 is more correspondence than is common in New Hampshire, in this sec- 

 tion, between the topography and the stratigraphy. 



Represented upon the map, upon the east side, is part of an oval area 

 of porphyritic gneiss, ten miles long, lying in Chesterfield and Winches- 

 ter chiefly. It will be specially described in the next chapter. It is 

 regarded as older than, and hence underlying, the Hinsdale gneiss. In 

 Northfield, boulders of this rock are extremely common, enough to sug- 

 gest that it may be found in place there beneath the alluvium. If so, the 

 length of the oval area would probably be doubled, and thus extend much 

 farther south than the Bethlehem group, which barely reaches into 

 Massachusetts. These two older series do not join each other visibly, 

 because their boundary is covered by extensive developments of mica 

 schists and quartzite. 



The structure of this gneiss is like that of the Hanover area, mostly 

 inverted, but the general inclination is reversed from that, being easterly 

 rather than westerly. The following are observed positions : 



Verno7i. West of E. P. Brown's, 70° E. 



Near L. F. «Sc G. F. Gould's, school district At west edge of formation, near school- 

 No. 4, 45° S. 20° E. house No. 7, 70° E. 



Farther west, 55° southerly. Hinsdale. 



At school-house No. 5, 40° E. On Elmore's island, easterly, the same as 



West of railroad, between the church and at Cooper's point. 



the Whithed family cemetery, sever- At school-house No. 4, east. 



al ledges, 65° E. South of E. Ashcraft's, about N. 70° E. 



Between the church and Vernon station on East of D. Fisher's, vertical ; strike about 

 railroad, 55° E. north and south. 



This region was averaged by E. Hitchcock At S. E. Butler's, east. 



at about 30° E. Between F. Thomas's and Bear hill, east. 



