GEOLOGY OF THE CONNECTICUT VALLEY DISTRICT. 2/9 



schist, and sandstone. For twenty rods beyond, the rock is purely horn- 

 blende, and is three hundred feet thick. The strata are concealed for 

 one hundred and eighty rods along the line of section, which must be 

 2400 feet thick, if their inclination agrees with those upon both sides. 

 Just beyond is a black slate, exposed at a railroad crossing at the north 

 end of Lisbon village, which is the last member of the series, and it has 

 been traced along the strike for ten miles, from the south part of Lit- 

 tleton to the line of Haverhill. The total thickness of the Swift Water 

 series on this section seems to be over 4400 feet. 



The Lisbon group begins a little east of the village of Lisbon, and 

 reaches into Lyman. The following are the kinds of rocks seen : first, 

 hydro-micaceous conglomerates, — 756 feet; second, hydro-mica schists, 

 with cupriferous layers, — 3539 feet. The upper division often carries a 

 nodular mass of nearly white quartz, from fifty to one hundred and fifty 

 feet thick. A little to the south of the line of section, and observed very 

 largely elsewhere, is an aggregate of feldspar and chlorite. It is the 

 same with that adjoining the Helderberg rocks in Littleton. The fault 

 which has nearly cut off the Lyman group on the section has caused this 

 rock to disappear beyond the south corner of Lyman. 



The Lyman group has a thickness of only two hundred feet adjacent 

 to the fault. It is entirely wanting a quarter of a mile farther north. 

 Beyond the slates it has a thickness of 2330 feet, allowing it to be folded. 

 The clay slates next succeeding are 1500 feet (possibly 1800) thick. They 

 contain the well-known auriferous quartz vein worked at the Dodge mine, 

 yielding, in its better parts, from $15 to ^25 to the ton. They resemble 

 closely certain auriferous rocks of Nova Scotia, referred to the Lingula 

 flags of Great Britain by A. R. C. Selwyn, geologist to the Dominion of 

 Canada. In composition it resembles the Lyman schists, and may have 

 been derived from the breaking up of the latter. A study of the struct- 

 ure of the Cambrian slate over the Ammonoosuc area shows it to be a 

 synclinal. I have followed it carefully, from the unmistakable basin form 

 in Bath, to the inverted monoclinal dip of the section line. There is 

 very little variety of lithological character in this series. 



After passing the slates, the largest area of Lyman schist in this field 

 presents itself. Near its eastern border are large lenticular-shaped beds 

 of quartz, some of them thought to be auriferous, and certainly associ- 



